I assume that you want to do it on your computer (rather than the old-fashioned, but perfectly usable, way of editing onto tape).
The first thing you'll need to do is to get the CD tracks onto your hard drive. The 'CD ripping' function within Windows Media Player can do that job for you.
Then you'll need some audio editing software. This is the freebie that most people use:
http://audacity.sourceforge.net/download/
You should note that, in its native format (because of licensing issues) , Audacity doesn't let you export filers in MP3 format. You need to install the LAME MP3 encoder to fix that problem:
http://audacity.sourc...install&item=lame-mp3
Then download the user's manual, which will explain what you need to do from there:
http://audacity.sourc...t/help/documentation.
Unless things have changed since I was in teaching, your local authority will require you to show that you've got the relevant licence before you can use any copyright music in a school production.
Chris