In the case of a horse pulling a cart, the horse exerts a force on the ground in the direction opposite to the direction in which it wants to move.
According to Newton’s Third Law, the ground will then exert an equal and opposite force on the horse in the direction opposite to the force exerted by the horse. This force is commonly referred to as the “ground reaction force.”
This ground reaction force is what allows the horse to move forward. As the horse continues to exert a force on the ground, the ground exerts an equal and opposite force on the horse, propelling it forward.
The horse’s feet push back against the ground, and the ground pushes the horse and the cart forward.
So, while the horse is pulling the cart, the action is the force that the horse exerts on the ground, and the reaction is the force that the ground exerts on the horse, allowing it to move forward and pull the cart along with it.