Newton’s Third Law states that for every action, there is an equal and opposite reaction. These forces always occur in pairs and act on two different objects.
When you walk on the ground, your feet exert a force on the ground, and the ground exerts an equal and opposite force on your feet. It is this reaction force that causes you to move forward.
One of the most well-known examples of this law is the motion of rockets. Hot gases are expelled downward at high speed, and in reaction, the rocket moves upward.
This law shows that a force never exists alone, and interaction between two objects is always the cause of motion and physical changes.