First of all you'll need to go here:
"<Steam Install Location>\Steam\steamapps\common\Counter-Strike Global Offensive\csgo\cfg"
Once there you'll have to make a new file called autoexec.
cfg, the best way is to make a new notepad document, open it, then save it as "autoexec.
cfg" with the file type selection box on "All files (*.
Then open this blank document in notepad, then that's it, you have a blank autoexec.
You can now either fill it with your own commands you wish to run every time the game starts, use mine from the next section or another person's.