In the upper left corner there's a button that toggles between wav-editor and multi-tracker. That's the first step. Then just right-click on the track to insert a WAV file (presumably you have two), then right-click and drag to move them to sync them up. Or, popup on them, select "Wave block properties", and change the offsets that way.
When you're done, select all, go to edit->mixdown to file (all wavs) and it'll output a single stereo wave file.
Cool?