A lens hood is a black plastic surround that clips onto the front of the lens. It's purpose is to prevent stray light entering the lens from the side angles and causing unwanted optical effects. It can also help protect your lens in that if you drop it and it lands on it's front, the hood will take most of the impact instead of your lens hitting the ground directly and getting smashed up.
A filter is a thin piece of glass in a metal ring that screws directly onto the front of a lens. They come in many different types, UV and polarising included. It can be argued that a UV filter provides little optical benefit on a digitial camera because the sensor is not as sensitive to UV as wet film is. However, many people still use them to provide protection for the front lens element. It's far cheaper to replace a scratched filter than a scratched lens.
Polarising filters are considerably more expensive than UV filters. You probably wouldn't use one just for protection of your lens. They help reduce glare and reflections, as well as making the sky look a deeper blue and making colors look more vivid in general.
I myself use hoods and UV filters on all my lenses, and also have a polarising filter for use with my 17-85mm which I swap with the UV filter only when I need it.
If your kit lens is the EF-S 18-55mm, then an appropriate lens hood is the Canon EW-60C, and a basic UV filter is the Hoya UV(0) HMC 58mm.
Hope that helps. I'm a newbie to photography, so someone else may be able to give a more accurate answer.
Jason