2) Your electric guitar has a wooden neck, and a wooden body. There are metal strings that are pulled tight, anchored at the top of the neck, and the lower part of the guitar body (the "saddle"). When the strings vibrate, like when you pick them, they make a very quiet sound that resonates through the body of the guitar. This quiet sound is "picked up" and amplified by a magnetic coil which is wrapped with copper wire. The "pickup" converts the vibration of the strings into an electric signal which then travels through the rest of your electrical components in your guitar body (your volume and tone "pots") and then heads out via your guitar cable to your amplifier.
"Single Coil" guitars, such as the famous Fender Stratocaster and Telecaster use a pickup or multiple pickups that only have one coil. This produces a distinct sound, but also allows a lot of hum and unwanted noise to be picked up, most noticeable when the guitar is not being played but the volume is still up.
"Humbuckers" are a type of pickup that use two magnetic coils which phase out any unwanted noise. The guitar will remain quiet when not played, even when the volume is up. The Gibson Les Paul is a very famous humbucking guitar.
Single Coil guitars have a bright, sometimes referred to as a "bell like" tone. They really stand out. They are favored by Blues players, but used by all kinds of artists.
Humbuckers have a rich, thick tone. In my opinion, they sound "meatier" than single coils. They are favored by Rock, Heavy Rock, and Metal players, but are used by all types of artists.
There are no rules. You'll find all kinds of styles using lots of different types of setups. Also, there are plenty of "here's a humbucker that sounds just like a single coil" and "here's a single coil that sounds just like a humbucker" technologies out there. Some people want a guitar that has the latest in pickup technology, others want a classic instrument, which is why companies like Fender and Gibson offer "re-issues" and "vintage" models, as well as state of the art ones.
