set up a git repository

I have been trying for the last few hours to set up a git repository and it's driving me nuts.
I really tried hard in a lot of different ways. I tried with gitbox and source tree but i have the idea it's also possible from within intelliJ.

What i want is that my project appears on github. I allready have it on my hd.
Where do i start?

I could post in detail what i tried but it's so much that it will be a wall of text and images.