Compression tester is a pressure gauge that fits into a spark plug hole. They come with instructions.

But if the engine runs nicely, don't worry about it. Maybe just change your oil incase some dirt got into it.

One ghetto check is take off your oil filler cap with the engine running. If your compression is bad, lots of oily air will blow out of the hole. Some of that is almost normal, so if you've never done that you might not know how much is normal.