We have quite a few written tutorials on sidechaining. In this screencast, we revisit the topic in video form, so you can see how the technique works first hand. But we revisit it with a twist, demonstrating how you can use it with different processors, and to create dynamic returns.
View this tutorial on Audiotuts here:
http://enva.to/16Tf8mL
Explore more tutorials on sidechaining here:
http://audio.tutsplus.com/tag/sidechaining/