Thevenins Therom

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Could you please explain to me about thevenins therom, how it works and how to use it.

Thevenin's Theorem for electrical networks states that any combination of voltage sources, current sources, and resistors with two terminals is electrically equivalent to a single voltage source V and a single series resistor R. So the complex circuit can be simplified via the Thevenin's Theorem.

The equivalent circuit can be obtained by using the following steps:

(1) Calculate the output voltage, VAB, when in open circuit condition (no load resistor - meaning infinite resistance). This is VTh.

(2) Calculate the output current, IAB, when those leads are short circuited (load resistance is 0). RTh equals VTh divided by this IAB. The equivalent resistance can also be obtained by the following steps:
(a) Now replace voltage sources with short circuits and current sources with open circuits.
(b) Replace the load circuit with an imaginary ohm meter and measure the total resistance, R, "looking back" into the circuit. This is RTh.

The equivalent circuit is a voltage source with voltage VTh in series with a resistance RTh.

Here is an example: Use Thevenin's Theorem to simplify the following circuit.

Step 1: Calculating the equivalent voltage VAB.

Step 3: Calculating the equivalent resistance:

Now we need to short the voltage source.

Thus, the equivalent circuit of the original circuit is

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