When transferring WAV files from the Stadium app to the device, each WAV file becomes one track in the Song. You can transfer up to 8 WAV files at a time, meaning up to 8 tracks in a Song. If you transfer a single file you get a Song with a single track.
The tracks are not editable after transferring in either the app or the device, at least not in the same way they can be edited in, say, a DAW. You have minimal editing capabilities on the device, and none in the app. For instance, you can rename tracks, or move tracks up/down to reorder them. But you can’t, for instance, create split points to create an audio gap by deleting between split points, or to create two new tracks by splitting/dragging audio clips into a different track. You need to do that sort of editing on your computer before transferring the WAV files. You might be able to drag a track to reposition the audio in the Song, for instance if one the WAV files should only be heard in the Chorus; I haven’t tried that.