Do you mean you downloaded a Passbook-enabled app and it doesn't appear in Passbook? The apps themselves don't appear in Passbook. Instead, the apps are able to add passes to Passbook. For example if you had a mobile boarding pass in the app, you might be able to add it to Passbook and then have it appear on the lock screen at the appropriate place and time.
Remember, you also don't need an app to get passes, they can also be added to Passbook from email or the web. Also, once you have a pass, you can still get back to the app store room at itunes.com/passbookapps.
I have downloaded the Starbucks app, it doesn't appear within the Passbook app. Don't know how to place it with the other app.
Are you saying that the apps are seperate icons and let's say that I downLoad a boarding pass within it, I can then program that boarding pass to show up in the Passbook application? If this is the case how?
For the Starbucks case, I believe you have to create a Starbucks account and then either add value with your credit card or enter the information for an existing physical Starbucks card. I don't think you can add the card to Passbook unless you create a Starbucks account.
See http://www.zdnet.com/how-to-add-your-starbucks-card-to-passbook-7000005214/ and comments where they say an account is required.