How to start git-gui?

Type git citool to start git-gui.

If it gives the error: git: 'citool' is not a git command, just install the following package: git-gui

sudo apt-get install git-gui

Typing

git gui

should work. Without dash.

In terminal type :

git gui citool

Make one commit and return to the shell when it is complete. This command returns a non-zero exit code if the window was closed in any way other than by making a commit.

 git gui citool --amend

Automatically enter the Amend Last Commit mode of the interface.

git gui citool --nocommit

Behave as normal citool, but instead of making a commit simply terminate with a zero exit code. It still checks that the index does not contain any unmerged entries, so you can use it as a GUI version of git-mergetool.

Reference Site