what is half life alpha half life alpha was a very early version of half life i dont know too much about it but there is a wikipedia i would recommend you to look at
https://half-life.fandom.com/wiki/Half-Life_Alpha#:~:text=Half-Life%20Alpha%200.52%20is,purchased%20later%20for%20%24709%20USD.

to download half life alpha you need to first download n glide that emulates an old computer graphics card (you don't need to download this if you are using a windows 95 with a graphics card)
(download link)
http://www.zeus-software.com/downloads/nglide

you also need to download half life alpha itself (you don't need to own half life for this)
https://www.moddb.com/downloads/half-life-1-alpha-052

now that you downloaded and did the things you need to go to n glide and set up your resolution for example 1920x1080 resolution

and now that you've set up n glide extract all the files from half life alpha

half life alpha has a bunch of files and videos that show gameplay and stuff here's the videos all videos have been upscailed and stuff but the videos are really low resolution there are also some .txt files but i wont show you any of them ill let you the reader do that yourself

now that you have done everything now its time to play the game open the file named half life gl and that will launch the game now you can play half life alpha!

so now the controlls
e- is to move forwards
d-go backwards
s - strafe left
f- strafe right
and the mouse stuff still applies

space- jumo
ctrl- crouch
b- use button

q – toggles invulnerability
r – toggles invisibility

z - make gun visible
x - make gun invis

n - noclip

h - fullbright
j - turns off full bright

l - toggles trace lines

1 - flashlight
2-4 -guns (you also have to press mouse 1 to select gun)
5-0 - makes sounds
backspace - stops cd from playing

m1- fires weapon and selects weapon
m2 - second weapon fire
m3 - spray

tab- slowmo
shift - normal motion

restart - restarts the level

maps – lists all the maps in the valve\maps directory
map techdemo - takes you to the very beginning of the E3 demonstration
map maindemo - takes you to the doors right outside the room with the seal on the floor
map silodemo - puts you in the room out in front of the green tentacle monster
map c1a3 – map with a bunch of grunts and the fan puzzle
quit – good for escaping the occasional ugly situation

now you have installed half life alpha now you can play it and stuff have fun

while researching for this guide i found a better guide that tells you a lot of things about half life alpha and i used the guide for the controlls part of the guide i would recommend you to check out the following guide
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1102835249