It gives you a nice, low-impact aerobic exercise, and allows you to travel useful distances w/o contributing to pollution.
Pants, a shirt, socks and shoes, a helmet and cool dude gloves (cool dude gloves are optional), oh don't forget the underwear
It helps, by not using the car for short journeys. But we in the West need to do much more to cut fossil fuel use.
First you need to make sure you aren't trespassing, then that your bike is up to it. Try to hook up with a riding buddy or make sure that someone knows your route in case you'd have an accident....
Wear a helmet and/or knee pads (arm pads will also work). keep your eyes on what is ahead of you. don't go to fast.