Hi Rae,
The humming would seem to indicate that the motor is running, so hopefully that's a good sign. So if the motor is indeed running, then that just leaves a couple of parts; there's a tension roller that tightens the belt against the drum, and of course, the belt itself. Here's a parts page showing all of the internals of your dryer.
[link|https://www.searspartsdirect.com/model/3kqtfm5rx6-001198/whirlpool-wed8620hc2-dryer-parts|Official Whirlpool WED8620HC2 dryer parts - Sears PartsDirect]
This page shows the belt, the motor and the idler pulley.
[image|3491143]
Part #37 is the pulley located on the motor itself; you'll want to verify it's not loose on the motor shaft and spinning freely; that would keep the whole thing from working.
Part #30 is the tensioner that tightens the belt so it grips tightly on the drum. If it's broken and not holding on, it could let the motor run without moving the drum.
And finally, of course there's part #34, the belt itself. If that's broken or fallen off, etc., then you'll get the behavior you're seeing. You might check YouTube for videos showing you how to replace the belt (which should also let you know how to get to the other parts to check them). The reviews for the belt mention that the replacement procedure is rated easy to very easy, so hopefully that's a good sign for you.