The cylinder head sits on top of the block. It's the thing directly below your valvecover that the intake and exhaust manifolds bolt to. No one really sells aftermarket Honda heads outright, you usually send your head off to get ported or machined. Pulling and installing a head isn't hard, but it may be a little more than you can handle if you're a "n00b." Typical headwork costs about $900 just for the labor, not including removing/installing the head.