You can start exploring the TTCatalog sample project that comes with the tri20 library. I am currently working with an improved version of tr20 created by Rodrigo Mazzilli, you can find it here ( http://github.com/rodmaz/three20 ). The rodmaz version is the plug from the original project, and it contains some improvements, especially in TTLauncherView. It has a new class called TTLauncherViewController, which is easier to use, see its TTCatalog demo project.
http://three20.info/ is a good site to work with some tutorials, but at the moment it does not have much information about TTLauncherView.
Finally, you should join the 320 google group at http://groups.google.com/group/three20, where you will find hundreds of developers using this library.
it's better