Plucking

Plucking is the use of tweezers to pull out hair, one by one, by the root. It is most common for the eyebrows and stray facial hairs.
A pair of tweezers is the only requirement, preferably a good pair over 3" long with a slanted tip for better control.

PLUCKING - HOW TO DO IT
First of all, assess your brows and the type of result you want. Don't fight your natural hair pattern, work with it. Accentuate the parts you like, downplay the parts you don't. Typically you should only pluck from the underside of your brow, aside from stray hairs which sometimes grow up the temples.
Once you have a rough idea of the shape you want, it's time to start plucking.
Grip the hair close to the base, and pull firmly with the grain. Do not quickly "yank" as this may snap the hair off, breaking it above the root. If you do it right it should be only mildly painful. Do not pull against the grain as this is very painful and not necessary.
It's best to go slow, plucking a couple hairs at a time and checking your progress frequently. Overplucking is unsightly, and if done frequently will damage the roots over time, causing your eyebrows to grow back more sparsely and slowly each time. The idea is to shape your brows to flatter your existing shape, not create a new shape altogether. Keep this in mind and you'll be on the right path to finding the best look for you.

PLUCKING VERSUS OTHER METHODS
Plucking is very cheap, and can be done by yourself at home, or wherever you may be! This is different than methods such as waxing, which is usually done professionally. However, plucking does require an eye for shapes. This doesn't matter as much when simply plucking a few stray hairs, but if you're looking to change things drastically and haven't got an eye for art, you may want to look into having it done professionally rather than wind up looking like Marilyn Manson(unless that's what you're going for!)
Also, plucking does involve some mild pain, but not as much as waxing or other methods which involve masses of hair removed at once.