ok...
pickups r generally two type in electric guitar. single coil, and humbucker... single coil is single, eheh... and humbucker is double coil. single coil has better treble and sustain, great for low distortion or clean. and humbucker its opposite. its generally rocker or metalists choice. single coil has the hum problem in cons. (the noise because of the radio signal around it, and u can easily solve the problem with shielding, whatever...) the humbucker kickin hum's butt, so thats why its called humbucker. (so it has no need to shieldin, its noiseless)

u can combine different pickups, like HH, HSH, SSS... combinin different type pickups with serial, paralel, in or out of phase generated unique tones. also the angle of the pickup is important. if u examine strat's bridge pickup, u'll notice its slant...