iTunes Connect will give you crash reports, although exactly how and when isn't particuarly clear. We've found it say there are none even after a refresh and then come back the next day and tried and suddenly reports are available and not for crashes occuring during the last 24 hours. Also it only happens for users who opted to automatically send diagnostic data to Apple.
The .crash file you can download from iTunes Connect is opened by xcode.
Apple Resources
Understanding Crash Reports
Good Resources
stackexchange.com/questions/1418/can-someone-help-me-read-this-crash-report-as-a-user
Basics
This tells you what the crash was and where it occured:
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Subtype: KERN_INVALID_ADDRESS at 0x5000000c
Triggered by Thread: 0
So now find that thread in the information below (the other threads are likely to be irrelevant):
Thread 0 Crashed:
0 libobjc.A.dylib 0x39710626 objc_msgSend + 6
1 UIKit 0x3156f50a __32-[UIActionSheet _slideSheetOut:]_block_invoke + 58
2 UIKit 0x313b73c2 +[UIView(UIViewAnimationWithBlocks) _setupAnimationWithDuration:delay:view:options:factory:animations:start:animationStateGenerator:completion:] + 494
3 UIKit 0x314dc9ba +[UIView(Internal) _animateUsingSpringWithDuration:delay:options:mass:stiffness:damping:initialVelocity:animations:start:completion:] + 142
4 UIKit 0x314dc91a +[UIView(Internal) _animateUsingSpringWithDuration:delay:options:mass:stiffness:damping:initialVelocity:animations:completion:] + 86
5 UIKit 0x3156f49a -[UIActionSheet _slideSheetOut:] + 426
6 UIKit 0x3156f25a -[UIActionSheet dismissWithClickedButtonIndex:animated:] + 1074
7 UIKit 0x313b7052 -[UIApplication sendAction:to:from:forEvent:] + 86
8 UIKit 0x313b6ff2 -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 26
9 UIKit 0x313b6fcc -[UIControl sendAction:to:forEvent:] + 40
10 UIKit 0x313a2732 -[UIControl _sendActionsForEvents:withEvent:] + 370
11 UIKit 0x313b6a4a -[UIControl touchesEnded:withEvent:] + 586
12 UIKit 0x313b671c -[UIWindow _sendTouchesForEvent:] + 524
13 UIKit 0x313b16e6 -[UIWindow sendEvent:] + 754
14 UIKit 0x313868e8 -[UIApplication sendEvent:] + 192
15 UIKit 0x31384f92 _UIApplicationHandleEventQueue + 7098
16 CoreFoundation 0x2eb31258 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 12
17 CoreFoundation 0x2eb30726 __CFRunLoopDoSources0 + 202
18 CoreFoundation 0x2eb2ef1a __CFRunLoopRun + 618
19 CoreFoundation 0x2ea99f0a CFRunLoopRunSpecific + 518
20 CoreFoundation 0x2ea99cee CFRunLoopRunInMode + 102
21 GraphicsServices 0x339bf65e GSEventRunModal + 134
22 UIKit 0x313e5168 UIApplicationMain + 1132
Finding the cause in that thread
Do you have a line like this (not from the above)? If so the :72 is a line number in the source .m code file:
1 stickskater 0x000642c5 -[GamePlayLayer init] (GamePlayLayer.m:72)
It can be really hard to determine the cause of crashes from these reports. Consider usign a 3rd party tool or adding a tool liek crashlytics to your application as it can make it soooo much easier.