How to connect a microphone to apply audio signal to electronic circuit?
Electret microphone capsules are very easy to use. Just give them a bias voltage and amplify the output signal. They have a built-in JFET that does the hard work. Here is an example schematic (from Sparkfun). 



Many electret mic capsules are available, with slightly different size, pedigree and frequency response. The 2.2K RL is more-or-less standard.