Kirchhoff's Voltage Law - KVL

Kirchhoff's Voltage Law states that the total voltage around a closed loop in an electrical circuit must be zero. If a circuit contains more than one close loops then the total voltage in all the individual loops must also be zero, this signifies that electrostatic field is conservative.

A detailed explanation can be read in this link with good examples and figures :

http://www.physics.uoguelph.ca/tutorials/ohm/Q.ohm.KVL.html