Newtons third law is all about action-reaction forces between the bodies. When two bodies interact with each other the force put by the first body (action) is equal to the opposing force by the other (reaction).
Newton's Third Law of Motion Examples
The rocket propulsion is the best example for this. Here the rocket gives out the hot gases with the force. This force is equal and opposite force that pushes the rocket in the opposite direction.
When we sit on the chair we apply downward force on the chair that will be equal to upward force exerted by the chair.