If you know anything about beer, you know one of the main ingredients is hops. Hops look like tiny green pine cones that grow on vines. Originally, hops were used as a way to preserve the beer. That is how India Pale Ales (IPA) were developed in the 18th century. British brewers would add a lot of hops in order to perserve their ales on the several month long trip to India. Now we know that hops do much more than just perserve the beer.
Hops balance out the sweetness provided by the malt sugars, and gives beer that somewhat bitter, but refreshing taste. Most of the bitterness comes from the alpha acid resins in the hops, while the flavors and aromas come from the oils in the hops. There are two categories of hops: bittering and aroma. Obviously, bittering hops give your beer the more bitter character, while aroma hops give your beer the flavor and aromas you experience.
There are a few different times in the brewing process, mainly the boil, when you want to add hops. Usually the bittering hops are added in the beginning, and boiled for the entire boil. Hops can be added midway through the boil in order to give the brew more flavor, and any type of hop can be added, its all up to you. Toward the end of the boil, more hops are added, called finishing hops, in order to savor more of the aromas and tastes. Hops may also be added to the fermenter, in a process called "dry hopping", to give the beer more aroma and flavor.
There are a bunch of different varieties of hops, and its up to you to find out what type you like to use, although sometimes flexibility may be an issue. Cheers!
