So, first day with the new Martin, decided to tune and take some on line lessons. While tuning the G chord, string snapped, scared the hell out of me and dropped the flippin guitar! Now on the lower body of the guitar, the top has a slight opening where it meets the side. What do I do?
If the top has come loose near the point of impact, or if any of the braces have come loose, you should probably take it to a luthier for repair. Unless you know a bit about glues and lutherie, I would encourage you to not attempt your own repair job in such a case.
It may be that only the binding has cracked, in which case you can probably just continue to play it. If you hear new rattles when you are playing, you'll know that the guitar needs some work. In any case, even if the guitar appears OK, it might be best to let a luthier take a look at it when you get a chance; they can repair the binding by splicing in a new section and tell you if it needs more work done.
This is kind of a bummer at the beginning of your journey, but in the future remember that strings break. They rarely pose any danger or cause any harm; get used to that happening (although I can't remember the last time I broke a string), and maybe wear a strap to prevent accidental droppings.