After I type in git commit -a a text editor pops up and I type in my comment. What buttons do I have to press after typing in the comment, to get it to move to the next stage of actually committing?
I'm using mysysGit on Windows with the default setup.
Depends on the text editor you are using. Git chooses the editor specified in the environment variable "EDITOR." On Linux systems this is usually either Vi or Nano. Figure out which it is and then refer to the documentation for the appropriate editor.