When one gets the ever popular "such and such" app has stopped, you get offered the option to report it. What are you supposed to say in the "report"?
You'll want to help the developer to help you.
mbanzon's answer mentioned that the developer will receive the stack trace of the error, but that only tells us what went wrong and where.
It does not tell us anything about the state the application is in: What was the value of that number, or what was the text that was entered in the text fields? And most importantly, what did the user exactly do to make the application crash?
The latter question is especially important so that we can reproduce the error, and help us understand why the application crashed under these circumstances.
So if you want to really help the developers, write down what you did, what you expected, and what you saw. For example:
I started the app and pressed the button to go to the reports screen. Then I pressed the button to generate the report, and the app crashed. Interestingly, the screen was blank: there was no data visible.
If you don't like typing much, you can be short:
Pressed button to generate report. Screen was blank.
If you have any information that would help identify the problem it can be a nice addition and help the developer much. If you are playing music via bluetooth and the music app crashes when you switch to a different bluetooth speaker and you experience this every time you switch speaker it would be useful to write "happens when I switch bluetooth speaker" eg.
The developer gets a complete stack trace of the error (only for the code in their app) and that would in many cases be enough to find and resolve the error.
As a developer, normally I get messages along the lines of "It crashed" which doesn't help me in any way. I would actually encourage you to not supply a message unless you can explain how to reproduce it (eg, if you can make it crash by doing something specific in the app).
Us developers also get a dump of technical information, which is normally more useful that a message saying where it crashed. Eg, the technical information tells us the exact line of code that it crashed on, and a lot more that pretty much tell us exactly what happened.
So basically, if you don't have anything to say about the crash, just submit it without a message and it will still be just as useful.