I put two songs but they start playing at the same time, why?

In the editor you can add up to 2 audio tracks that will play simultaneously. It is meant to add a music track and a voice over for the video. You cannot have two music tracks playing back to back.

A great solution is to combine two videos, each with its own soundtrack, into a third video. 

Another option is to loop your audio. You can find this option by clicking on the down pointing arrow (right side of the green bar).