What do Capacitors do?

Capacitance is the amount of charge that can be stored at a given voltage by an electrical component called a capacitor.

Capacitors: Reservoirs for Electricity After resistors, capacitors are the second most common component in the average electronic device. Capacitors are interesting little gadgets. They store electrons by attracting them to a positive voltage. When the voltage is reduced or removed, the electrons move off. When a capacitor removes or adds electrons to the circuit in this fashion, it can work to smooth out voltage fluctuations. In some cases you can use capacitors combined with resistors as timers. 

Capacitors make possible all kinds of circuits, such as amplifiers and thousands of others. Capacitors are used for all sorts of neat applications, including Creating timers: A kind of electronic metronome, a timer most often pairs up with a resistor to control the speed of the tick-tick-tick. Smoothing out voltage: Power supplies that convert AC current to DC often use capacitors to help smooth out the voltage so that the voltage stays at a nice, constant level. Blocking DC current: 

When connected inline (in series) with a signal source, such as a microphone, capacitors block DC current but pass AC current. Most kinds of amplifiers use this function, for example. Adjusting frequency: You use capacitors to make simple filters that reject AC signals above or below some desired frequency. By adjusting the value of the capacitor, it’s possible for you to change the cut-off frequencies of the filter.