After you have your song arranged and mixed in the Song Bar (at the top of theRiffWorks "rack"), save the song. Then I ususally "save as" another file name like"my song_mix1.rws so you don't mess with the riff arrangement.
Now you have to click on the Mix button and select Mix To Riff. This will record all the riffs in the song bar into one riff. You will see the new riff called MixToRiff.
Drag this up to the song bar and then drag all the other riffs out of the song bar.
Now click the Info button on the new Bounce layer in the lower (layer) window.
You will see a wave form that you can then adjust to create a fade in / out by grabbing the part of the riff that you want to fade. Hold down your right mouse button while dragging it across and down to the left until you get to the beggining of the riff. Drag from left to right the same way to create a fade out at the end of the riff. It should look like this when you are done:
