Pickups are one of the most important factors in the tone of an Electric Guitar. The pickups are what actually translate the vibration of the strings into an electrical signal. They operate by creating a magnetic field that the strings vibrate in. This vibration is turned into an electrical signal which is translated back to an audible signal by your guitar amp.
Pickups consist of a magnet, six poles, and lots of wire windings. The poles are placed on top of the magnet, and a small gage wire is wrapped around the poles, this is considered a single-coil pickup. It is important to understand how the pickups are made because this affects how they sound. The tone of any pickup is determined by the type and strength of the magnet, the number of windings, and the type of poles (i.e. Fixed or Adjustable Poles).
There are two major categories of pickups, single coil & humbucking pickups. Humbuckers got their name because when you pair two pickup coils with the magnets situated on opposite poles, it removes the hum that is produced.