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Off-Topic:- "Which mic is the best out of…?"(a.k.a. X vs Y), "Which mic should I buy with $1,000?", "My mic is broken/won't turn on, please help!", "I'm trying to talk to my team on Skype, but my mic cuts out"
On-Topic:- "What type of mic should I use to capture a lion's roar outside?", "Do switchable polar pickup pattern mics lose any quality?", "What is impedance and why do I care when buying a microphone?", "Why does the X/Y stereo technique stop phase issues?"

The Microphone

Microphones come in all shapes and sizes and can capture anything from a simple human voice to sounds inaudible to the human ear. In the sound industries, microphones are usually the very first device in the production chain. This makes them an extremely important part of the process, as mistakes made during this initial step can be impossible to fix later.

How do they work?
The microphone is a type of sensor which senses information from the physical world and turns it into a more useful form which allows further action to be carried out on the signal. Actions like amplification, storage and manipulation.
Fundamentally, microphones turn kinetic mechanical energy into electrical energy. This kinetic mechanical energy exists in the form of sound waves (pressure variations) propagating through a given medium (e.g. Air). This energy is sympathetically transferred to the microphone's element, inducing a varying electric current, whose wave shape is analogous to the original compression and rarefaction in the given medium.
The current is induced by different means for different microphone types. How precisely the original sound is represented by a microphone is known as the fidelity.

Note: A device, which converts variations into an electronic signal and vice versa, is a type of transducer. So, microphones and speakers are opposite forms of transducer.

There are three main types of microphone;

• Dynamic
• Condenser
• Piezoelectric

Each of these microphone types are suitable for different situations. Dynamic microphones are relatively robust, while condenser microphones are more sensitive, meaning they must be handled with care. Piezoelectric microphones are good for capturing sound in challenging environments, like underwater.

To learn more about microphones and the different types, visit the following links:
Microphone - Wikipedia
Microphones - artsites.ucsc