apt-get install git-core 

Run once to create your local work branch

git checkout -b  

Then make changes and commit to local branch.

Commit good practices:

• If you commit with git-gui, please inspect diff of every file included in the commit. You should not modify or delete any files that are not part of logic changes related to a task.
  If you do not have a gui program to commit, inspect diff from command line: git-status – check files that need to be added/removed and git-diff to inspect changed files.
• Enter a good description for commit: first line should be a  summary up to 80 chars, other lines can contain more descriptive message, if commit is related to a ticket use re #ticket_number to automatically add a comment to the ticket with commit description.

To push to repository:

rake git:push

this command will update code from remote repository and will rebase your work branch with master, merge master branch  and it will push your changes to remote server.

To update the code from central repository

rake git:update

git checkout master
git checkout -b  

commit your changes and after push this branch to remote

git push origin  

• You want to copy one commit from other branch to current branch

  git checkout current_branch
  git cherry-pick sha_id_from_other_branch
  

  Using gitk: 

  1. right click on current branch and click check out this branch from popup menu
  2. click on commit from other branch, right-click and select Cherry-pick this commit
• You forget to add some files to previous commit:

  git reset --soft HEAD^
  # do some changes, add files that you forget
  git commit -c ORIG_HEAD
  

  Using git-gui:

  1. Click Amend radio button above text area for commit description
  2. Add/remove files from commit
  3. Commit new changes

You can find more information regarding the Git here.
You can also find some useful miscellaneous git tools here