Let us understand the superposition theorem with the help of an example. The circuit diagram is shown below consists of two voltage sources V1 and V2.

First, take the source V1 alone and short circuit the V2 source as shown in the circuit diagram below:

Here, the value of current flowing in each branch, i.e. i1', i2' and i3' is calculated by the following equations.

The difference between the above two equations gives the value of the current i3'.

Now, activating the voltage source V2 and deactivating the voltage source V1 by short-circuiting it, find the various currents, i.e. i1'', i2'', i3'' flowing in the circuit diagram shown below

Here,

And the value of the current i3'' will be calculated by the equation shown below:

As per the superposition theorem, the value of current i1, i2, i3 is now calculated as:

The direction of the current should be taken care of while finding the current in the various branches.