Reminder : GIT HOW-TO for GitHub

Download and install Git
git config --global user.name "Your Name"
git config --global user.email myadress@mail.com

Next steps:

mkdir PNG2CSS
cd PNG2CSS
git init
touch README
git add README
git commit -m 'first commit'
git remote add origin git@github.com:louisvolant/PNG2CSS.git
git push origin master

Existing Git Repo?

cd existing_git_repo
git remote add origin git@github.com:louisvolant/PNG2CSS.git
git push origin master