First of all create a local repository in the preference folder with:
git init
This will create a .git in the folder for git to recognize as a repository.
The flow I learned was this:
Clone the repository:
git clone https://github.com/meunome/meurepositorio
After this the flow is as follows, there is the "Working Directory" that is where your files are, the "Index" that is the temporary area (where you will use git add) and the "HEAD" that is like if it was the area that sends it back to the online repository.
You basically make the changes where you want, add the changes with
git add *
And then commit to the "HEAD":
git commit -m "comentários das alterações"
It will be in the "HEAD", to send back to the source repository:
git push origin master
It is a very generic example that I put, based on the pt-br guide, but that's how I learned it.
Source: link