Theros

I did read damage rules several times from Champions Complete book. I think that those are rather hard to understand complicated. I understand that every attack does stun damage and dices that roll 2-5 inflict one point body damage and 6s inflict two points body damage. Then...right? When body goes to zero, then that character or opponent starts vleed to death (he loses body every phase or?). Then...killing damage. How that is inflicted, how it is calculated? Of course killing damage (RKA?) goes through PD and ED. Only resistance will help to prevent damage. Then question from DCs (damage classes)...that is rather confusing too. Why those are needed?

I am going to take my players to Champions universe and play as super heroes there. What kind of books are needed to offer solid experience? I haven't played or GMd Hero System earlier, but I have quite long experience from GMing. I would start with necessary things (max three books). Also where to buy? I prefer hard copies over pdfs.