How do I overlap songs?

Okay, so lets say i have three tracks that are different guitars to one song.
how do i put them together so they all just play at the same time???

Use the Time Shift tool to drag each track to where you want it.

– Bill

no, i mean how do i put them together into one track??

You don’t need to. All tracks are automatically mixed into a single stereo file when you Export (or a mono file if all the tracks are centre panned mono track).
Audacity does not “Save” audio files - the “Save” function creates “Audacity Projects”. To make an audio file that can be played in other programs you use “Export”.