http://media.putfile.com/JDUB-cork-5
alright, watch that video. Now while you're watching, notice how he takes his left shoulder and throws it back (or "drops" it) and then he rotates over top of the dropped shoulder. Thats what is meant by "drop your shoulder".
Sorry thats a kind of sloppy cork 5 but the best I could do for right now. Slow it down or watch it frame by frame if you have to, to understand what we mean. Just watch that left shoulder when he's at the lip. But that should give you a basic idea.