Where or How to edit DEPOT_PATH

hello
could you tell me what step you did?
i read it but i dont know what i need to do, I can’t find any video to help, it’s too hard to visualize, please help me.

could you please take a moment to make a demonstration video for me, i have read that article, but i don’t understand how to do it, i don’t know what is environment variable? i don’t know how to config or setup

maybe i have to give up julia, no one helps me.