iN008: This is going to be really basic but I'll try to explain without being too complicated/too simple.
Each team has 5 members- your jammer [the one who scores] 3 blocks [people who block] and your pivot [which isn't really important if you just want to know the basics]. The bout starts with both teams packs [4 players to each] starting on the track, with the jammers 30 feet behind them. The goal is to get your own jammer through the pack and to lap them once. Each player you pass, you receive a point. What makes it difficult is that the other team's jammer is also trying to break through. So you have 4 members trying to keep her back while trying to help you through; but the opposite team is doing the same thing. There are other rules like Lead Jammer who can call off the jam [round] at any point [when you see a jammer hit their hips with their hands] but basically- you win by how many points your jammer receives during the jam. That probably didn't make much sense so if you wanted a more in depth telling - http://www.pioneervalleyrollerderby.com/for-fans/derby-101/
marcushoward : Teach you? I can't teach you through words on a computer screen
If derby were easy- everyone would be doing it. There wouldn't be broken bones, bruises, concussions and paramedics waiting on call with stretchers during every bout. There is technique, you have to have skills & know how to do certain things to qualify as a roller derby player.
1) Balance. A lot of people can not step out onto a rink floor [I work at a roller rink lol, I've seen it with all ages, people can't skate] and suddenly know how to keep perfect balance on 8 moving wheels.
2) Technique. Holding corners, hugging curves, knowing how to play a gap, being able to see what is going to happen before it happens.
You have to look around you, analyze what is going on while keeping an eye out for your jammer and to see what the other team is doing. It's requires a lot of focus and a lot of concentration. You don't have time to think about anything else except; can I hit this angle? Can I power around that corner or do I need to hold it? Can I get through that gap? It's a puzzle that is constantly changing, there is never a scenario that shows up twice.
3) It is a real sport. Yes, we wear glitter and fishnets and hotpants and we look ridiculous. [Whip It has not helped us out in that area] but we are athletes. We train, we practice, we have to stay fit, we have to receive physicals to receive clearance to do this. No one can just hop out onto a track and say "WOO, ROLLER DERBY GIRL!"
4) There are a lot of injuries. It's not something easy that you walk away from with a scratch here and there. Girls get concussions, broken bones, busted faces, bruises, paramedics are standing by at most bouts for this reason. People get hurt. Granted, injury or risk level doesn't give a sport its validity but many people think that its just a bunch of girls messing around and wearing short skirts. But we get hurt, we have to know how to fall, how to get up from a fall; because there is a very big risk factor involved.
You are entitled to your opinion. You don't have to think it's a sport, you can think it is boring and stupid and easy and every other demeaning term in the book that you could associate with what we do. But the fact is; it's hard work. We train, we put blood, sweat and tears into what we do; it is so much more than just going around in circles and wearing some flashy clothes. But maybe you don't believe that; and like I said; that is just fine!

But don't judge how easy it may be unless you have some level of personal experience~ That's all.