How do you cut music out of a song to make it shorter?

Open iTunes. Right-click on the song you want to shorten. Click "Get Info." Then click "Options." There, it'll show "Start Time" and "Stop Time." Adjust the time you want it to start the song and stop it.

There are innumerable other ways of editing or manipulating a song to make it shorter too. If you know exactly what you want to cut out then audio production software such as Cubase and Pro Tools will let you do this. There are cheaper alternatives to those programs too such as Goldwave and Reaper.

If you have apple you can use garage band program and edit.