This is covered in your manual, and extensively in the forum posts in the Nikon section of this forum. I suggest you try a search there. The differences are also explained on many websites if you try a google search.
i suggest you get this book D80 digital field guide by david d.busch. Its a full colour guide which tells you everything about d80 and how to use all the available functions. Also include how to shoot scenarios like fireworks, sunset, portraits and many others. Only cost $34, can get at borders or kinokuniya. Else you can borrow from the library books on exposure.
Read up your D80 user manual. I'm sure nikon will use the classic example of a sunrise pic to show how center-weighted metering works..
For those instances, center-weighted is used because you don't want to overexpose the sun; anything else can be underexposed.