I’m a new electric guitarist and can you explain what pickups are?

An electric guitar or bass pickup is an electromechanical device for tracking the vibration of a moving string made of ferrous material. The string attracts the magnetic field from within the pickup and when plucked the movement of the magnetic field through the coil(s) causes an electrical current to be generated. The signal is connected to an amplifier by means of a shielded single or multiple conductor guitar cord and reproduced over a loudspeaker.
The basic construction of a guitar are bass pickup are:
1. A permanent magnet usually of Alnico or Ceramic material used for magnetizing the string to be plucked thus generating an electrical current.
2. The pole pieces can be either rods, bar, screw or other means of conducting the magnetic field to the ferrous strings.
3. The bobbin can be a support for the pole pieces, coil and means of mounting the pickup.
4. A coil wound with a variety of magnet wire and desired number of turns
5. A bottom plate used to elevate or mount the pickup.
6. A cover is used for coil protection or means of supporting the components of the pickup inside the cover. Depending on the material used a cover can also be used for reducing unwanted electrical interference especially on humbuckers.
Basic info on single coil on Fender style pickups:
1. 6 cylindrical alnico rod magnets of a determined diameter and length. North or South top polarity for magnetic phasing.
2. Top and bottom flatwork usually made of Vulcanized Fibre. The top is usually .062” thick and the bottom is .093 inch thick. On pickups such as Jazzmasters, P Bass, J Bass the top and bottom are both .093 inch thick.
3. 2 eyelet’s for soldering the beginning and finish coil wires and connecting the hookup wires that connect to the control plate. The beginning of the coil is normally connected to the black or ground connection. The finish of the coil is normally hot.
4. Coils are wound in a clock wise or counter-clock wise direction for electrical phasing of two or more pickups.
5. Hook up wire used to connect the electrical current from the pickups to the control harness on the pickguard or control plate.
6. Single coil pickups are usually potted in a wax solution to help eliminate unwanted microphonics and feedback normally associated with playing at high volumes or using pedals that overdrive the signal to the amplifier.
7. Single coil pickups are prone to hum and unwanted electrical interference due to stray magnetic fields from amplifier transformers and florescent lights.
8. The increased number of turns on a single coil pickup will increase output and reduce highend. Over-winding pickups can make them sound muddy but with increased sustain.
9. The thicker the magnet wire the less turns can be put on a bobbin. The thinner the magnet wire the more turns can be put on a bobbin.
10. Single coil pickup can be made magnetized two ways (north or south) and wound two ways (clockwise or counter-clockwise) making 4 ways a single coil pickup can be made.
11. Pickups can be wound for bridge, middle or neck position. I call this calibration for better balance between positions.
12. Single coils can be RW/RP, reverse wound/reverse polarity so when two single coil pickups are used they will be humbucking or quieter in the selected position.
13. Single coil pickups shielded by a copper foil can eliminate a small amount of unwanted (RF) electrical interference but not hum that is generated by stray magnetic fields.
14. To help keep single coils quieter a shielded conductor from the coil to the controls should be used.
15. Single coils guitars can be noisier due to the larger transformers being used in modern amplification. Older amps with smaller power and output transformers produce less stray magnetic fields from the amplifier.
16. Single coil pickups with exposed coils should always use a cover to avoid damage to the delicate winding in the coil.
17. Magnet wire used for the coil is copper wire coated with a protective insulation to keep the turns from shorting or bare copper from oxidation that would result in failure in the coil.
18. Reversing the magnetic field in a single coil will magnetically change the polarity in the pickup. Reversing the hookup wires in a single coil will electrically change the polarity in a pickup. Reversing the hookup wires can make the magnets noisy when touched by your fingers.
19. Single coil pickups can be hand wound. Hand winding is usually when the magnet wire is guided on by hand when turned by a winding device. Automatic winding is when the coil machine has an automatic traverse to guide the magnet wire back and forth on the bobbin.
20. Hand winding has a haphazard number of turns per layer and number of layers. Automatic winding gives you a precision number of turns per layer and number of layers. Used with controlled tension the coils will be more consistent from pickup to pickup.
21. Rod magnets should not be moved within the coil on vintage pickups as the coil is wound directly around them. Movement can break the inner winding of the magnet wire causing the pickup to fail.
This is just a few things of interest with pickups