You can simply get out by EXIT (29), but if you want to keep the current "environment" of CLASS , e.g. all the parameters defined by SET commands, use the SAVE command (28), which writes the corresponding SET commands on a command file (here IC348.CLASS). Later you will be able to re-execute all these commands and rebuild the previous environment, by entering : @ IC348, thus avoiding a lot of tedious typing.
That's it, you now know (nearly) everything. Good luck...