It's built-in to the New Curve, and all you need to do is set up a Blackberry ID to be able to access App World.
Unlike Android, where any app is allowed, for the most part, you will only be able to add the apps that Blackberry allows on App World. With Android, there are malicious apps that can steal your personal information, and apps that cause problems with battery life, mess up Android processes, and generally cause chaos.
Blackberry avoids this problem by only allowing reputable apps.