Supermoon is an astronomical phenomena which occurs when the moon is at its closes orbital point (Perigee) to earth while being is a full moon phase in the same time. Since the moon is orbiting earth in an elliptical orbit, it seems a bit bigger when it is closer to earth.
How much bigger, not much, about 14% from its “smallest” orbital phase. While the difference is hardly noticeable to the naked eye, it makes a great excuse to bring those tele-lenses out and have a fun night photographing the moon. But it will also be 30% brighter which can help in making shorter exposure / lower ISO shots.
This illustration from Wikipedia demonstrates the average difference in moon size from a regular night to a supermoon night.
Here is a great moon photo take at the supermoon of March,19,2011
P.S. You should feel pretty safe in your back yard for shooting the moon as its proximity is unlikely to cause any earthquakes or title waves.