iOS In-App Purchasing step by step tutorial

Is there any step by step source code/video or any othe开发者_如何学Cr kind of help to implement in-app-purchasing ? I have tried many tutorials but still i am not able to get perfect solution for the in-app-purchasing..

What is the use of shared secret key?

I think that the best guide ever is the official In App Purchase Programming Guide, since it's full of examples, piece of codes, hints and so on. Following and reading carefully the Guide will surely help you in writing a fully functional test project.

In the meanwhile you could want to look at the MKStoreKit v4 add-on for your project to help you handle your in-app purchases in a easier way.