In the past, there's been a standard roller derby explanation video that I've seen at bouts:
However, it's literally the basic rules, and doesn't really get into a lot of the strategy, or why people do what they do in a pack. There are other pretty simple rules that explain that.
Here's a video that Rose City put together which sums THAT up pretty well, as well as with the basics:
Plus, it also says Roller Derby > pretty much every North American sport, so yeah. Enjoy, and learn!