There are two ways a project and GitHub meet:

Clone — copy an existing GitHub project onto your machine:

git clone https://github.com/someone/their-project.git

Create & push — put a project you started locally onto GitHub:

git init                        # start tracking this folder
git add .
git commit -m "First version"
git remote add origin https://github.com/you/your-project.git
git push -u origin main         # upload it

After that first push, sharing new work is just git add ., git commit -m "...", then git push. Your code is now backed up and visible to the world (or just you, if the repo is private).