Add these to your launch parameters:
-noqt -usevgui -sfmcomicmaker
Then, go up to Windows->Engine Window->Uncheck Auto Hide Engine Window.
This will allow you to use the engine window, which is usually hidden by default.
//WARNING\\
If anything bad does happen to your SFM session (Which is very unlikely) just know that it is NOT my fault.
\\END OF WARNING//

To start, you'll obviously want to right click>Create comic.
This will create the first page of your comic, which will be 1920 pixels wide and 1080 pixels tall.

Make whatever scene you want, then right click and select the most obvious item: Add panel from sequence.
"Wait? Why 'from sequence'?"
This is so that you can add multiple panels quickly. Once you add all the panels you want, you might notice something...
"Why is there panels missing?"
The comic maker can only fit 4 panels in one page.
Open the page switcher in Windows>Comic Page Transport.
Each page is numbered

You might've noticed a window pop up when you tried to create a panel in the last section, that is the Element Editor!
This editor is specifically for editing the properties for pages/panels.

Comic maker thread: https://steamhost.cn/steamcommunity_com/app/1840/discussions/0/864977564253899282/
Also according to the thread: Narry Gewman takes all the credit for discovering this stuff. caseytube wrote the thread. I wrote this guide.