It's difficult to tell you what settings when we don't know anything about the lighting in the room...
The lighting in the room is critical; most church weddings I've been to have relatively low lighting. And at many weddings, flash photography is frowned upon (besides the fact that few flashes can reach the altar from more than a few rows back in most churches). If you don't know much about ISO settings, now may be the time to learn. Increasing your ISO settings will increase the sensitivity of your camera, making low light shots easier to take - at the expense of noise and/or graininess in the photo.
But, like Gail said, it's hard to give much advice without more information...
