Yosemite Climbers

Right now, two climbers are, literally, hanging on the sheer face of El Capitan, a rock wall in Yosemite National Park. Their names are Tommy Caldwell and Kevin Jorgeson, and they are attempting one of the most difficult free climbs in the world: The Dawn Wall route up El Capitan. It requires scaling 3,000 feet of smooth granite. How are they going about the feat, and why?