"Audacity" Help Needed

Can anyone tell me the best way to add a second track in Audacity? I'd like to record harmonies and can't figure out how to do it.

I record the first track, then I should be able to record another one right over it, but I can't hear the first one and I need to hear it to sing along with it.

I'm working with a headset and mike now, but that creates a little feedback.

Any suggestions, ideas, words od wisdom will be greatly appreciated.

Thanks!

you can do file open and select an mp3

then you can highlight parts of it and copy and paste it into other windows

just do file>new and have a few audacity programs open imo