It's not any different than a regular guitar. It feels slightly different since you're pressing down on twice as many strings as you're use to... But you still play everything exactly the same...

I own an Ovation 12 string... I'm not a huge fan of Ovations but it was priced pretty well so I picked it up... It plays great and sounds great so I can't really complain.... Fender makes a nice and cheap 12 string as well.