Systemstate is basically made by the process state for all process in instance (or instances) at the time the systemstate is called.
Through a systemstate it’s possible to identify enqeues, rowcache locks, mutexes, library cache pins and locks, latch free situations, and other kind of chains.
It’s a good tool to add in a SR, but it’s quite hard to habituate on reading/interpreting the file. To undertand exactly how to read a systemstate I’d recommend you the best: Read the manual!
The doc Reading and Understanding Systemstate Dumps (Doc ID 423153.1) has a very good explanation with examples, I’m not able to to it better. 🙂
What I can do is share about the SYSTEMSTATE levels. I had some difficult to find it…
But before I show how you can do it, it’s important to mention that Oracle does not recommend you to use ‘numeric events’ without a SR (MOS), according to Note: 75713.1.