From what I have found is once you add something to Passbook you will no longer see the same screen that you saw when you first opened the Passbook app. If you add more than one card you should see all of the cards that you have added on the same screen that you see the one card you have already loaded.
You can find the list of apps you first saw the first time you went into the Passbook app by using your iPhone to go to the app store. Under the featured section at the top scroll to the right until you see the icon labeled "Apps for Passbook." Click that and you will see the same apps that was listed on the screen of the Passbook app itself. I don't know if Apple intended for this to be this way, but unless they change things you can't get back to the main screen within the Passbook app itself. The "Apps for Passbook" will not appear if you do the search from an iPad.