A Capacitor is a component that stores energy in an electric field. It does this by having two plates seperated by a dielectric. This is called capactitance and is measured in farads (F).
Capacitors are resistant to changes in voltage, and therefore can be used to smooth out sudden changes. They also cause AC signals voltage and current to get out of sync.
Different types of Caps are useful for different applications, simply based on the materials present in the cap.
When Capacitors are in series, the total capacitance comes to be the reciprocal of reciprocals. This means that the total capacitance for Capacitors C1 C2 and C2 would be
Total = 1/(1/C1 + 1/C2 + 1/C3)
When capacitors are in parallel the values of capacitors are added together. This means the total capacitance of a set of parallel capacitors is euqal to the sum of their capaciatance