The crash.* functions are actually not that complex to work with. If a crash occurs the engine will write crash data to disk. What you typically do if you wish to track crashes is that you call crash.load_previous() when the app is started. If the function returns nil it means that the app didn’t crash on the previous run but if you get a crash handle back you can use it to read the data and send it to some service for parsing (don’t forget to release/delete the crash after it’s sent!).
My Google Analytics lib has built in crash reporting: