git gui Add hunks, write the message, add more hunks, write more message. Once you are happy commit it, close the window. Don't try to use the CLI only because

git gui Add hunks, write the message, add more hunks, write more message. Once you are happy commit it, close the window. Don't try to use the CLI only because you are a power user who only uses the command line. If you really can't use the gui (like your on a remote SSH session or something), the non-gui equivalent is git add -p, write your message in another editor, then git commit -F message.txt