I wrote this guide to help people get comfortable with ScriptableComputer API. Lua knowledge will be useful, because it replicates the Scrap Mechanic Lua API[scrapmechanic.com]
At the moment this mod is still in development, it has some bugs and issues, but they are not critical.

Press [E] to open block interface. There will be 2 textboxes: script editor and error details. Also, there are 2 buttons: DONE - save script, CLOSE - close without saving. GUI is not synchronized in real time, so don't press DONE, when your friend is editing the script, because your friend will kill you.

Connect ScriptableComputer to the trigger and activate it to start up the computer.

Place CompositeWriter and CompositeReader, connect Writer to Computer and Computer to Reader. You have to specify the register names in Writer and Reader, Reader will be read from a specific register and Writer - write value into.
For example, you may specify K in reader and K1 in writer.
You have created the logical inverter!

If you activate the reader and remove it, you can see that the writer's signal doesn't change. It happens because register values are saved between ticks. If you restart the computer, you also can see that the writer is off. If you print the variable input, it will be nil (nil == 0 will return false), this means the computer will set K1 to false.

Let's write the tick generator. Connect computer to the logic gate.
If you turn on the computer, logic gate with be activated one time in 10 ticks.
What is TIMER = TIMER or 0? This defines a variable.
When TIMER is nil,
It will look like this:
    First tick - TIMER == nil: nil or 0 == 0
    Next tick - TIMER == 1: 1 or 0 == 1

This program measure the angle as xo-meter from modpack. ScriptableComputer mod is compatible with modpack and you can connect the computer to number blocks to output value in radians, or convert it into degrees. You can use this mod to improve speed of calculations or to make cheat programs. It's up to you ;)

Script environment has more interesting custom functions:
getParentComputers()
getChildComputers()
getDisplays()
getMotors()
getRadars()

You can use registers to connect computers together, but this method has a problem: big delays. You can connect computers to each other and use API to get globals from env directly.
Parent computer:
Child-connected computer:
Now if you activate both computers, you will see numbers in chat. First printed value may be nil, but may be 1, because of the SM block updating order. After loading from lift, this order can be changed, so you need to write optional if to check is shared value not nil.

data = {
env, -- environment of computer
registers -- registers of computer
}

Displays are very laggy. You should know that.
Connect the computer to some display.
Code:
If you connect quite big display, you will see some yellow text.
Function clear() is time-consuming for big displays. If possible, use fillRect() to clear color in a special region.

data = {
getWidth(),
getHeight(),
clear(color),
drawPixel(x, y, color),
drawRect(x, y, w, h, color),
fillRect(x, y, w, h, color),
drawCircle(x, y, r, color),
fillCircle(x, y, r, color),
drawLine(x, y, x2, y2, color),
drawText(x, y, text, color),
optimize(), -- optimize image if you don't want to use clear method for a long time
flush(),

setClicksAllowed(bool) -- activate | deactivate sensor screen,
getClicksAllowed(),
getClick() -> { 1: x, 2: y, 3: "pressed"|"drag"|"released", 4: 1|2 }, -- last number is 1 when "E" button and 2 when "U"
setMaxClicks(n: int [1; 16]), -- sets the buffer size
getMaxClicks(),
clearClicks(), -- clears the click buffer

setRenderAtDistance(bool), -- calculate rendering of pixels not rendering, can break well-optimized rendering
getRenderAtDistance()
}

data = {
getVelocity(),
setVelocity(num),
getStrength(),
setStrength(num),
getAngle(),
setAngle(num | nil),
isActive(),
setActive(num | bool)
}

Radar can't be used to detect static objects (because of API issues). Method getTargets() returns targets array. Every target contains 5 values: body id, horizontal angle, vertical angle, distance and signal force (depends on mass and distance). Angles are in [-pi, pi) and depend on radar shape local coordinates system.

data = {
getTargets(), -- returns array of { body id, hangle, vangle, distance, force }
setAngle(num),
getAngle(),
setHFov(num), -- (0; pi]
getHFov(),
setVFov(num), -- (0; pi]
getVFov()
}

data = {
getMaxPacketsCount(),
getPacketsCount(),
nextPacket(), -- give next packet to process
send(str),
clear() -- clear buffered packets}

data = {
createFile(path),
readFile(path),
writeFile(path),
deleteFile(path),
hasFile(path),
getFileSize(path),

createFolder(path),
deleteFolder(path),
hasFolder(path),

getUsedSize(),
getFileList(path),
getFolderList(path),
openFolder(path), -- change default tracing path (e.g. cd)
getCurrentPath()}

Lets write simple code
Calling display.optimize() is so important in such case, because camera render image pixel by pixel and you need to optimize screen quadtree for better performance. Also you can draw something above camera picture. You may write 'display.drawText(0, 0, "hello", "eeeeee")' after calling some camera draw function. Calling display clear function in that sutiation is wrong, because you will get colorful stripes (only if the render step isnt big enough).

data = {
drawColor(display),
drawDepth(display, baseColor),
drawColorWithDepth(display),

setStep(int), -- sets the rendering step (how much pixel will be rendered at draw call)
getStep(),
setDistance(num),
getDistance(num),
setFov(num), -- when low it has more details, when high it has more coverange,
getFov(),
getNextPixel(), -- get pixel camera starts render from
resetCounter(), -- reset that pixel to 0}

This template can make coding easier. It provides 4 general methods/callbacks (onStart, onTick, onStop, onError).

• print(str) - print in chat
  
• debug(str) - print in console
  
• tostring(v) - see[www.gammon.com.au]
  
• tonumber(str) - see[www.gammon.com.au]
  
• getreg(name: str) -> [number | bool] - get value from register
  
• setreg(name: str, value: [number | bool]) - set value to register
  
• clearregs() - clear all registers
  
• type(val) - see[www.gammon.com.au]
  
• assert(cond: bool, msg: [str | nil]) - see[www.gammon.com.au]
  
• error(msg, level: [num | nil]) - see[www.gammon.com.au]
  
• pairs(table) -> (function, value, nil) - see[www.gammon.com.au]
  
• ipairs(table) -> (function, value, 0) - see[www.gammon.com.au]
  
• next(table, index) -> (index, value) - see[www.gammon.com.au]
  
• pcall(f, ...) -> (num, ...) - see[www.gammon.com.au]
  
• xpcall(f, err) -> (num, result) - see[www.gammon.com.au]
  
• self - link to ScriptableComputer script
  
• select(index, ...) -> ... - see[www.gammon.com.au]
  
• global - link to global namespace
  
• getParentComputersData() - deprecated, use getParentComputers
  
• getParentComputers() -> table - returns table of parent computers datas
  
• getChildComputersData() - deprecated, use getChildComputers
  
• getChildComputers() -> table - returns table of child computers datas
  
• getConnectedDisplaysData() - deprecated, use getDisplays
  
• getDisplays() -> table - returns table of child displays datas
  
• getConnectedMotorsData() - deprecated, use getMotors
  
• getMotors() -> table - returns table of child motors datas
  
• getConnectedRadarsData() - deprecated, use getRadars
  
• getRadars() -> table - returns table of child radars datas
  
• getPorts() -> table - returns table of child network ports datas
  
• getDisks() -> table - returns table of child discks datas
  
• clientInvoke(code: str) - performs invokation some code on clients
  
• input(color: [str | nil]) -> bool - input selector (if color specified); returns true if one on selected inputs is true else returns false
  
• ninput(color: [str | nil]) -> table[num] - if color specified returns table of parent interactable powers; if no color - returns full table of powers
  
• out(value: [num | bool]) - set power and active state of self.interactable
  
• loadstring(code: str, env: table|nil) -> function - make function from code
  
• execute(code: str, env: table|nil) - execute string code

• string.byte(str, index=nil) -> number - see[lua-users.org]
  
• string.char(num) -> str - see[lua-users.org]
  
• string.find(str, what: str) -> (start: num, end: num) - see[lua-users.org]
  
• string.format(format, ...) -> str - see[lua-users.org]
  
• string.gmatch(str, pattern: regex) -> function - see[lua-users.org]
  
• string.gsub(str, pattern: regex, replace, n: [number | nil]) -> function - see[lua-users.org]
  
• string.len(str) -> number - see[lua-users.org]
  
• string.lower(str) -> str - see[lua-users.org]
  
• string.match(str, pattern: regex, index: [number | nil]) -> str - see[lua-users.org]
  
• string.rep(str, n: number) -> str - see[lua-users.org]
  
• string.sub(str, start: number, end: [number | nil]) -> str - see[lua-users.org]
  
• string.upper(str) -> str - see[lua-users.org]
  
• table.insert(table, value) & table.insert(table, pos: num, value) - see[lua-users.org]
  
• table.maxn(table) -> [num | nil] - see[www.gammon.com.au]
  
• table.remove(table, pos: [num | nil]) -> value - see[lua-users.org]
  
• table.sort(table, comp: [function | nil]) -> table - see[lua-users.org]
  
• table.concat(table, sep: [str | nil], start: [num | nil], end: [num | nil]) -> str - see[lua-users.org]
  
• math.abs(num) -> num - see[lua-users.org]
  
• math.acos(num) -> num - see[lua-users.org]
  
• math.asin(num) -> num - see[lua-users.org]
  
• math.atan(num) -> num - see[lua-users.org]
  
• math.atan2(y: num, x: num) -> num - see
  
• math.ceil(num) -> num - see[lua-users.org]
  
• math.cos(num) -> num - see[lua-users.org]
  
• math.cosh(num) -> num - see[www.gammon.com.au]
  
• math.deg(num) -> num - see[lua-users.org]
  
• math.exp(num) -> num - see[lua-users.org]
  
• math.floor(num) -> num - see[lua-users.org]
  
• math.fmod(num, num) -> num - see[www.gammon.com.au]
  
• math.frexp(num, num) -> num - see[www.gammon.com.au]
  
• math.huge - see[lua-users.org]
  
• math.ldexp(num, num) -> num - see[www.gammon.com.au]
  
• math.log(num) -> num - see[lua-users.org]
  
• math.log10(num) -> num - see
  
• math.max(num, ...) -> num - see[lua-users.org]
  
• math.min(num, ...) -> num - see[lua-users.org]
  
• math.modf(num) -> (num, num) - see[lua-users.org]
  
• math.pi - see[lua-users.org]
  
• math.pow(num, num) -> num - see[www.gammon.com.au]
  
• math.rad(num) -> num - see[lua-users.org]
  
• math.random(m: [num | nil], n: [num | nil]) -> num - see[lua-users.org]
  
• math.randomseed(num) - see[lua-users.org]
  
• math.sin(num) -> num - see[lua-users.org]
  
• math.sinh(num) -> num - see[www.gammon.com.au]
  
• math.sqrt(num) -> num - see[lua-users.org]
  
• math.tan(num) -> num - see[lua-users.org]
  
• math.tanh(num) -> num - see[www.gammon.com.au]
  
• sm [full] - see[scrapmechanic.com]
  
• bit [full] - see[lua-users.org]
  
• os.clock() -> num - see[lua-users.org]
  
• os.difftime(t2: num, t1: num) -> num - see[lua-users.org]
  
• os.time(t: [nil | table]) -> num - see[lua-users.org]

• This mod is compatible with Modpack
  
• This mod uses Lua interpreter (not native, because of SM Lua api, thanks axolot) from this github[github.com], thanks to the author; also I tried LBI (with better performance as I tested) from ScrapVM mod, but it has problems with environment
  
• Because of interpreter, performance is worse than native in about 4-6 times
  
• Script performs every game tick (in fixed update)
  
• Script performs only at server, if you need to perform something on client, use clientInvoke(str)
  
• Registers and global variables save between ticks, but reset after computer turning off
  
• Script has iteration limit and you can't freeze the game
  
• Exceptions have a really bad tracing (but in the future it must be fixed)
  
• Displays are so laggy (in general 64x64 and upper, but last time so laggy is only render), if you place lot of high-resolution displays, pixels can start disappearing (because of SM effect limitations)
  
• Displays have 15 meter render distance
  
• Radars can't detect bodies, connected to map directionally

Please, report all bugs and issues in the comment section.