Help with setting up GitHub

I am learning how to code with PHP and when asking for coding help, often I see people recommending to use GitHub for coding examples.

I know nothing about GitHub, but thought I’d try to get it set up, but I’m completely lost with what to do. I’ve created a repository. That is it. I don’t understand where I create my php and css files.

Can anyone help me through the process of setting up what I need to give example code for others to help me with. (Or is there a different program I should be using that would be better for this?)

Thank you.

Github itself has awesome documentation on this: