Welcome to git and linux. Here are a few links to get you started
https://help.github.com/articles/set-up-git
http://git-scm.com/book
http://git-scm.com/book/en/Git-Basics-Getting-a-Git-Repository
http://zrusin.blogspot.com/2007/09/git-cheat-sheet.html
Git for beginners: The definitive practical guide
There are a couple of different ways to do this. The easiest in my opinion is the command line.
Open up a terminal, and cd to the directory that contains the android project.
cd /home/bob/foo
ls
Initialize the git repo, this will create a hidden .git file inside the folder
git init
ls -a
Create your first commit, by adding all files to the working tree
git add .
git commit -m "My First Commit"
You will now have a master branch, and 1 commit. You can veiw your commit with the following commands
git status
git log
If you aren't comfortable using the command line yet, you could alternatively accomplish all of this with a gui. Here are some programs for linux.
https://git.wiki.kernel.org/index.php/InterfacesFrontendsAndTools#Graphical_Interfaces