Maybe this will help (or maybe it won't!)....
In this picture I'm working on Riff4, it has 3 layers. If I hit the "duplicate" button on the upper left, it will give me an identical copy of the riff with a new name, that I can add to.

In this picture I'm working on riff7(1). In this case it's a completely different riff I created from scratch by hitting the "create" button in the upper left. To add more layers to a riff, just hit record and go!

I dragged all these riffs into the songbar up top, to create a song out of them. From there you can do a "mix to wav" and the song will be exported to a wav.
I hope something in there helps!