Usually a crash means you have some sort of memory problem or calling a undefined function(sending a message that is not answered by the receiver).
Are trying to read from a pointer to an object that was released already? Are you trying to send a message to an object that is not answering to it?
The good news is that you have a lot of good tools to find out exactly what it is:
First of all, open the console (Shift + Command R) and see if there is a message or stack trace when your app crashes. If there is no message, run the debugger (Shift + Command Y) and see where it stops on the crash.
Finally, if you see the status bar of XCode, it will tell you a bit of information about the crash (the message that was send about the crash, could be a EXEC_BAD_ADDRESS or some other thing.
Sadly, without your code or any of this information this is all I can do to help you. I would suggest not only copy and pasting but really understanding what that code is supposed to be doing and also learning how to debug your code.
For good resources I would recommend the Itunes U Standford Iphone development class and/or reading a good book about it(I read the Head First Iphone book and I love the series but didn't really like this one).