Launch the demo. Click on the Register from the menu. Click on Enter Registration Unlock Code. Enter your name and the code you received by e-mail when you purchased the game. This will unlock the game giving you access to the full feature set.
Hearts is a popular game, but it is quite complicated.
Championship Hearts Classic has an excellent tutorial to teach you the basics. The game should offer to launch the tutorial the first time you play, but you can also access it through the Help menu at any time. Each of the virtual players has a different playing style. This isn't the way I've played Hearts before. A screen will appear that lets you alter the way hearts are broken, who leads first, and what you need to shoot the moon.