Thevenin's theorem is a procedure by which we change a complex network in to simple network called thevenin's equivalent circuit.
Thevenin’s equivalent circuit of an open circuit voltage, thevenin voltage, Vth and the total resistance from the open terminals side, thevenin's equivalent resistance, Rth. Connected both thevenin's quantities in series. In this way we can find the current or voltage of any branch of the circuit.
Remove that resistance in which current is wanted
Find the open circuit voltage, VAB called thevenin's equivalent voltage, Vth.
Find the total resistance, from open terminals A and B side is called thevenin's equivalent resistance, Rth removing actual voltage source from the circuit.
STEP # 4
Connect Vth and Rth in series. This will be the thevenin's equivalent circuit.
Reconnect the RL between the open terminals of the thevenin's equivalent circuit.
Find the current in RL
As both resistances are connected in series so the in RL. and Rth are same.