Kirchhoff's circuit laws are important for circuit analysis. There are two laws: Kirchhoff's Current Law (KCL) and Kirchhoff's Voltage Law (KVL). KCL states that the sum of currents flowing into a node is zero: $$\sum_{k=1}^n I_k = 0$$
KVL states that the directed sum of voltages around a closed loop is zero: $$\sum_{k=1}^n V_k = 0$$