So, to recap: Musk wants his private spaceflight business to send 80,000 people to Mars every year. They're not going to do that themselves, probably, but the company would certainly be leading the charge.
How are they going to do that?
Well, as Talking Points Memo writes, one of SpaceX's big pushes is for reusable rockets. We've had something like that in the form of NASA's classic space shuttles, but the refurbishing, Musk has said, is too much to truly make repeat space-travel cost-effective. In the RAS talk, he says that technology is still some time away--maybe five to six years before we can fully reuse a craft.
Whatever that reusable craft for colonists is, it's not going to be a current SpaceX model, like the Falcon 9 rocket. They're going to need a bigger boat: shipping off a considerable amount of people and cargo isn't feasible with the spacecrafts we have now. (Even with SpaceX's 22-story Falcon Heavy rocket, capable of carrying 117,000 pounds.) The new spacecraft, whatever it looks like, would probably run on methane, which Musk determined was the cheapest option.