The trial allows you to play the game for free for seven days. If you want to continue playing after that, you can purchase the game online or in stores. You'll be able to continue using the character you created for the trial.
The seven day trial is open for players from North America, Australia and New Zealand. Europeans can go here for their trial version.
Smart move. People like free. Im giving it a shot. 4GB dl kinda sucks though.