.
A capacitor is a device that stores an electrical potential. It is composed of two plates that are separated by an insulator called the dielectric. When a capacitor is charged, the electrons from the positive plate move over to the negative plate, creating an electrical imbalance between the two plates. Overall, when a capacitor is "charged" this does not mean it is holding more electrons than when it is not charged, but rather the electrons have shifted from one plate to another.
Capacitors are measured in farads (F), which is defined as being able to hold one coulomb (Q, and is equal to 6.24*1018 electrons). This is a very large amount of energy, and most capacitors are rated in microfarads (µF) and picofarads (pF). The capacitance of a capacitor depends upon the size of the plates, the distance the plates are from one another, and the dielectric used. If the area of the plates increases, the capacitance will increase, but the capacitance will decrease if the distance between the plates increases. And if the material used between the plates has a higher dielectric constant the capacitance will increase.
If you put two capacitors in parallel it is like increasing the area of the plates. So putting capacitors in parallel increases the inductance, and the overall capacity is equal to the sum of the two capacities. But putting the capacitors in series is like increasing the length between the two plates, so when putting capactors in series the total capacitance is equal to .