Hops (Humulus lupulus) are green cones that are attached to vigerously climbing vines and are used as flavoring agents for beer. They can make your beer bitter, citrusy, and/or earthy (among many other characteristics) depending on the kind of hops you decide to grow. For example, classic American-grown hops include:
Hops are generally planted in the Spring and harvested in the Fall. Both professional and home brewers boil hops to release acids from their lupulin glands, giving your beer its distinct flavor.
To grow hops all you need is plenty of vertical space and a love of beer. Pergolas, arbors, or even just a long piece of wood stuck firmly in the ground attached to a string will give you the space you need to start your hop garden. While 1st year hops tend to be on the small side, 2 year hops will have you swimming in alpha and beta acids.