Kirchhoff's laws
Kirchhoff's current law
Kirchoff's current law sais that the sum of the currents coming into a node is equal to the sum of the currents leaving the node. In ohter words; if only one of the incoming or outgoing currents is unknown, one can calculate it's magnitude on the basis of the other currents. The sum always has to be equal to zero.
Kirchhoff's voltage law
Kirchoff's voltage law sais the sum of the voltages in a loop is always equal to zero.