Analytics Software

Hi,
I dont have much idea on the drill down. I have done a drill down on time dimension when I was undergoing training. That was pretty simple as it was year-quarter_month etc. But I have few questions on drill downs. My understanding is that we can create drill downs or hirearchies on dimension tables only. Am I correct? or can we create drill downs on fact tables as well. Can we create drill down for multiple dimesnsion table in a Subject Area. If we need an drill down option what requirements do we look for? like do we need only one dim table and decide what we need to drill down on. Please advice.