Microphones come in all shapes and sizes as well as price points. A microphone is essentially the opposite of a speaker. A speaker pushes and pulls on air, making waves that tickle our ears. A microphone receives sound and converts it to an electrical wave that can be amplified and can be sent into a computer, audio mixer, or public address system.
Microphones come in two major categories, with a couple of odd exceptions here and there.
The Shure SM58—the most popular dynamic mic in the world is as follows:
Dynamic microphones are the tough guys of microphones. They aren't usually delicate, due to the fact that they have very simple electronics. Dynamic microphones use a membrane to vibrate along with sound waves, moving a coil that is between two magnets. The vibration of the coil creates an electrical current that flows down a cable to be amplified. The amplifier used to boost the signal before sending that signal along to be used in recording is called a microphone pre-amp. The volume knob at the pre-amp is called a trim knob. This is what a dynamic mic looks like from inside:
The AKG Perception condenser microphone is shown as follows:
Condenser microphones have a very thin, flat conductive sheet called a diaphram that is suspended in front of an electrified backplate. Any movement of the diaphragm disturbs the electrical field between them, making a signal. Condensers then take this information and have a bunch of circuitry that convert the signal into something our audio interface would like. It still needs a pre-amp. The signal is usually very detailed compared to the dynamic mic. If you plan on screaming a bunch, the dynamic may be a better choice. If you are a crooner, you should think about getting a condenser mic (although they tend to be more expensive). Here's what the inside of a condenser mic looks like:
If you are just starting to record things, I would suggest investing in a dynamic mic from a company like Shure, AKG, or Electro-Voice. They are well established and you can find them online for pretty reasonable prices.