Capacitors: What Good Are They?
Capacitor is a passive electronic component that stores energy in the form of an electrostatic field. In its simplest form, a capacitor consists of two conducting plates separated by an insulating material called the dielectric. Capacitance is directly proportional to the surface areas of the plates, and is inversely proportional to the plates' separation.

Capacitance also depends on the dielectric constant of the dielectric material separating the plates.

The standard units of Capacitance;

farad: F

microfarad: µF (1 µF = 10-6 F)

nanofarad: nF (1 nF = 10-9 F)

picofarad: pF (1 pF = 10-12 F)
Capacitor as a Timing Element
Capacitor as a Coupling Element
Capacitor as a Filtering Element
Capacitors as Power Supply "Bypassing" Elements
Bypass Capacitors' Minimum Impedance at Self Resonance
Paralleling Bypass Capacitors for Maximum Effectiveness
illustration of the effects of Inductance due to Excessive Lead Length.