All right, I can help you with this OP, I've done this before.
First of all, know the beer, so that you can know what you like and do not like.
Your basic catagories are these:
Pilsner:
Clear, crisp, and golden yellow. Hops are more prominant than the malt taste, but they're pretty mild in general. The common Budweiser is a preverted descendant of this style.
Hefeweizer:
German style. Cloudly yellow and far from clear. They have a significant wheat portion, hence the name. The style tends to be tangy and citrusy and is often accompanied by a slice of orange.
A derivative of hefeweizen is the belgium white beer. Which maintains a cloudy and slightly citric flavor, but tends to be more mellow yet spicy. Blue moon falls somewhere between hefeweizen and belgium white.
Stout: Guinness is crap, but this is the style. Dark, malty, and sometimes peaty. Don't let the dark fool you, these beers tend to be sweet. They go great with food and lounging. They can vary quite a bit, but all have the flavor of toasted malts.
Pale Ale: India Pale Ale is the most common sub-type. These beers are all about Hops. This makes the beer quite bitter, but in a very rich and taste way. The color and thickness vary, but these are great beers. They are a little intimidating to new drinkers, but when you learn to love the IPA you are a full fledged beer snob.
There are more of course, but that's the basic rundown. Check out this site:
http://en.wikipedia.org/wiki/Beer_style