[assumes everything is installed]
cd ruby_rails  [ie, wherever you want to keep all your rails projects]
rails new_project  [create the project]
ruby new_project/script/server  [wow - your new app is up!]
[ctrl-c to kill it]

[in new_project dir, do]
git init
git add .
git status
git commit -m "Initial commit"
[need also git push if save to server, assumes new_project repository exists, if not first create it a github.com]
git remote add origin git@github.com:YOURGITHUBUSERNAME/new_project.git
git push origin master

[later... make some edits]
git checkout -b modify-README  [creates new branch named modify-README]
[edit some files]
[want to rename a file?] git mv README README.markdown
[new files?] git add .
git status
git commit -a -m "comment about what you changed"
git log   [show history]
git branch  [shows branch tree]

[merge]
git checkout master
git merge modify-README
git branch -d modify-README
[you would want the branch to be all done and tested before you merge it]
[sort of a Release Point]
git push