Describe situation where newton's 3rd law is operating?

Answer 1

The most common example is that you throw a ball at the wall, it comes back to you.

You do the action and then wall does the reaction by returning the ball with equal magnitude but in a direction opposite to your action.

Answer 2

When you sit on a chair, your body exerts a downward force on the chair. In response, the chair exerts an equal and opposite force upward on your body, allowing you to stay seated. This is an example of Newton's third law of motion in action.