For beginners. Really.
You run an application on your device and it crashes. You want to know what was the context of the crash and at which line of code the crash happens. Here is what I do to find out.
If the application uses library like CrashReporter (see previous post on similar subject: Processing user's crash logs (when symbolicate don't work)), you can get the crash report by email. Then, open Xcode's Organizer, select Archives. In my case, when doing a test session, I build my own Ad Hoc version of my app, then install it on my test device via a service like www.testflightapp.com (I could use Organizer too! But I really like TestFlightApp service). For that purpose, I build an archive.
Next, right click on an Archive then select Show in Finder. You'll see something like this.