Will Fly, thanks for pointing out that scissors icon. On my screen it's very easy to miss that, since it's a little light blue icon on a gray background, and it has a horizontal sound-wave-type design in blue behind it -- so at a glance, it looks more like a snowflake than a scissors.   
Now that I've found that, it's actually pretty easy to clip my mp3. You just play the mp3, which has numbers at each point above, and note the beginning and end numbers. Then click on the scissors (open/close editor) icon, highlight the section you want to copy or cut, then pull down the edit menu to click on copy or cut (or you can use the normal key strokes for copy, cut, paste, etc.). Piece of cake.

This part of Garage Band is easy. One of these days (weeks, months) I'll have to spend some time learning all the other neat things you can do with GB.    (I gather I can do all the things with it that I do with Finale NotePad Plus, and more.)

Thanks, everyone,

Genie