Thomas
Toward the front of the owner's manuals for most keyboards are diagrams of the main panel and back panel with all the buttons and connections listed, usually with a very brief description of what they do, and sometimes with a manual page reference for further info. That should give you a start, but there is not much you could do by pushing buttons that would hurt anything. The worst you could do is generate a factory reset that might erase some "freebies" (tones, songs, rhythms, etc) that came on the machine from the factory, but the typical factory reset requires that you hold down a combination of two or more buttons or keys as you power the keyboard on, so not much chance you would do that inadvertently. Besides, in a lot of cases, a factory reset is how you bring back things that were factory installed. As far as normal button presses that would erase or overwrite that same type of data, the keyboard will ask you if you are sure you want to do that. If you get that type of message and are not sure where it is coming from, just answer "NO", or hit the "EXIT" button, or at worse, just power the keyboard off than back on. There are only about two things that you can do from the front panel that could cause any kind of real physical damage: turning up the volume until it blows out your speakers and/or ear drums and turning up the display brightness to the point that you may shorten its life expectancy. Everything else is pretty much "try it and see if you like it". The main point is not to become afraid of it. For the most part, you can't hurt anything, and you learn most by "pushing the buttons", so have at it !
Best of luck !
Looking forward to seeing you over at the Casio Music Forums that Gary pointed you to above.