The first rule of underwater photography is to get close, then get closer. The tricky part is that most new divers need more experience to fine tune their buoyancy skills. If your skills are good, go right ahead. If not, having a camera would be a distraction.
What kind of photos do you want to take? Most shown on this board are either wide angle or macro. Using the camera only, you could do some nice macro and head & shoulders portraits.
If you want to start out easy and get some nice results in shallow waters, pick up a Magic Filter. You'll see all kinds of posts on Wetpixel about them. I would use aperture priority at f/5.6, ISO 100 or 200, and about -1/3 or -2/3 exposure compensation. There is a filter called the Auto Magic, designed for small cameras. It would allow you to keep your white balance setting on automatic. Filters are primarily for shallow water with good light.
Shoot JPEG. The other mode on your camera is TIFF, which will take forever to save and won't offer any practical advantages over JPEG.
Buy a book about underwater photography. It's a great way to learn about composition and technique.