stopped()

That method is called automatically anytime the user clicks on the 'Pause' button or a 'Greenfoot.stop()' method is executed. It is a World class method, so, therefore, it goes in your World subclass. It can be used to do anything that you want to do when the scenario is stopped.

How do I use it? Like this!?:

Of course.

It's not necessarily of course because this could just be like creating my own method with my own method name. And then in the act I'll have to call it: Just making sure (not misunderstanding between us): with this I'm NOT supposed to call in the act, right (gets called when stopped)?

It is not necessary to call it from anywhere, yourself. It is automatically called by greenfoot as stated above. That does not mean that you must not call it from the act or some other method. The code in it might be something that you would want to execute during run time, as well (the scenario will not stop if you call the method programmatically).

Take a guess.

When I put coding in it thinking it's a loop it didn't do what I wanted it to and I didn't see any other problems, so I asked and am still asking to make sure.

You can put whatever code you want in it; but is will only run once for each time the method is called -- and greenfoot automatically calls it one time each time the scenario goes from a running state to a stopped state provided that the method is in a class (or superclass and not overridden) that created the active world being stopped..