Designing a combinational circuit involves 4 steps. Let's break down each step in detail:

1. Problem Statement:
In the first step, the problem statement is defined. This involves understanding the desired input and output behavior of the circuit. It is important to clearly define the functionality and specifications of the circuit.

2. Truth Table:
Once the problem statement is defined, the next step is to create a truth table. A truth table lists all possible input combinations and their corresponding output values. The number of rows in the truth table is determined by the number of input variables in the circuit.

3. Boolean Expression:
Using the truth table, a Boolean expression is derived. This expression represents the relationship between the input variables and the output of the circuit. Various methods can be used to simplify the Boolean expression, such as Karnaugh maps or Boolean algebra laws.

4. Logic Diagram:
The final step is to design the logic diagram based on the simplified Boolean expression. The logic diagram represents the circuit's structure and the interconnections between the logic gates. Logic gates such as AND, OR, NOT, and XOR are used to implement the circuit.

By following these 4 steps, a combinational circuit can be designed effectively. It is important to ensure that the circuit meets the desired specifications and functions correctly for all possible input combinations. Additionally, the circuit should be optimized for factors such as speed, area, and power consumption.