i have done it twice on my a4, and i am not trying to be a jerk, but if you start with 'what is a wheel bearing' i would take it to an indy shop.i needed both a hub shark and a 20-ton hydraulic press (good luck using only a hub shark,) and you have to disconnect the abs sensor (not tough, but its apretty critical component.) plus you need to mark the washers so you dont lose alignment - otherwise you will need tohave that done as well.

its definitely something that needs addressed and shouldnt be ignored. jack your car up and wiggle that wheel back and forth to see how bad it is.