Don't mind these YeeHaws (myself included). Every newcomer gets razzed. The duplication of gears is a well-known and common phenomena. You can measure the gears on an inch-scale with a formula I can't currently remember. This helps to prevent this if you are re-building your drivetrain or just swapping out a cassette. Someone should come along with the formula.
Here are a couple of resources to get you familiar with the basics of bike-mechanics. The first one is a series of short videos giving demonstrations of many situations:
http://bicycletutor.com/
And this is the venerable Park Tool repair site. Just point to a part/area on the bike, and you'll get instructions:
http://www.parktool.com/repair/
And finally we have the personal site of Sheldon "Our Lord" Brown. Until recently, the greatest living resource on all-things bicycle:
http://sheldonbrown.com/harris/#articles
This should give you a good background.
Happy Trails!