Truth tables are created to easily display the inputs and outputs of logic circuits. They can show the inputs and outputs of a single logic gate to a complex circuit with multiple gates.
All truth tables consist of columns for input and a column for output. However, extra columns can be added to make the job easier and find the outputs of a logic circuit easier.
Truth tables for single logic gates are relatively simple. One or two columns for the input depending on the number of inputs, and a single output column.
Here is a truth table for a very simple NOT gate.

Truth Table: NOT Gate 
Input  Output 
A  X 
0  1 
1  0 

As you can see you list all the possible inputs, in this case only two, in the input column and then using the "math equations" or boolean equations given for each gate in order to get the output results.
This is a more complex gate with two inputs, the AND gate.

Truth Table: AND Gate 
Input  Output 
A  B  X 
0  0  0 
0  1  0 
1  0  0 
1  1  1 

Now we will show you a simple circuit with a few gates. This circuit has several steps. This is the final truth table based on the circuit on the right.

Truth Table: Circuit Gate 
Input  Output 
A  B  X 
0  0  0 
0  1  1 
1  0  1 
1  1  1 

This may be difficult to do in one step, especially if the circuits have even more different gates, which is why we can add extra columns into the truth table. After each gate in the circuit, we will give it another column. Here is the circuit with the new variables included. (The line over the A symbolizes a "not" in other words the line means to take the opposite of A.)
The new table will include a column for A(not) and M.
Here's the final truth table
Truth Table: Circuit 1 
Input  Sub Inputs/Outputs  Output 
A  B   M  X 
0  0  1  0  0 
0  1  1  0  1 
1  0  0  0  1 
1  1  0  1  1 
As you can see, finding the outputs one at a time is much easier then finding the final answer in one go.
Here's another example.
There are many more gates here, so there are more steps. Though this will take a longer time, it is not any more difficult. As always, first label the diagram after each gate using different variables. Here is a labeled version of the circuit. Remember that any variable can be used, but generally variables between the variables chosen for the inputs and outputs are used.
Now create the truth table with all the columns for different steps.
Truth Table: Circuit 2 
Inputs 
Sub Inputs/Outputs 
Outputs 
A 
B 
C 
D 
M 
N 
O 
P 
Q 
X 
0 
0 
0 
0 
0 
1 
0 
0 
1 
1 
0 
0 
0 
1 
0 
1 
1 
0 
0 
1 
0 
0 
1 
0 
0 
0 
1 
0 
0 
1 
0 
0 
1 
1 
0 
0 
0 
0 
1 
1 
0 
1 
0 
0 
1 
1 
0 
1 
1 
0 
0 
1 
0 
1 
1 
1 
1 
1 
0 
1 
0 
1 
1 
0 
1 
0 
1 
0 
0 
1 
0 
1 
1 
1 
1 
0 
0 
0 
1 
1 
1 
0 
0 
0 
1 
1 
0 
1 
1 
0 
1 
0 
0 
1 
1 
1 
1 
1 
0 
1 
1 
0 
1 
0 
1 
0 
1 
0 
0 
1 
1 
0 
1 
1 
1 
0 
0 
0 
1 
1 
1 
1 
0 
0 
0 
1 
0 
0 
1 
1 
1 
1 
0 
1 
0 
1 
1 
0 
0 
1 
1 
1 
1 
0 
0 
0 
1 
0 
0 
1 
1 
1 
1 
1 
0 
0 
0 
0 
1 
1 