The way I did it was like this:
1) create the repository
2) clone the repository on a new folder on your computer using
(git clone https://github.com/YOUR_USER/YOUR_REPOSITORY)
3) ctrl+c, ctrl+v your source into the folder you just cloned the repository into
4) using git bash (on windows) or any other git software you want (including git itself) do the equivalent of:
git add .
git commit -m "my submission to GameDev.tv GameJam 2022"
git push