I guess if your subject has bright sunlight behind him, you'd want to use spot/centre metering, using him as the object for metering. In this way, his face be correctly exposed, while the sun portion will be blown. If you chose average metering, the sunlight would be not be blown, but his face would definately be underexposed (dark).
For new user, I would recommend using the average or matrix metering of the camera as this usually yield good pictures about 80 - 90% of the time. However, if you have a particular subject that you want to focus on and you want to make sure that it is exposed correctly, you will use the center weighted metering (of course you have to make sure the subject IS in the center of the frame. If your subject is really really small, like a bird on a tree, you might even want to try spot metering.
Basically, average metering will cause the camera to look at the entire frame and average out the bright and dark areas of the scene. Center weighted metering will cause the camera to put more empahsis on the an area at the center area of about 30% of the entier frame. Finally, spot meter forces the camera to concentrate on only about 10 deg area from the center (some cameras will have a small circle in the center to let you know where this spot covers).