Sailor pushes water with the oar in backward direction. Consequently, the boat is pushed by water in forward direction. Hence, forces applied by oar and water are of equal magnitude but opposite in direction.
During swimming, a swimmer pushes the water backwards with his hands and legs. The water exerts an equal and opposite push on the swimmer’s body which, makes the swimmer to move forward.
The horse pushes the ground in the backward direction. The ground exerts a reaction force on horse and cart system to push them forward. When the raction force exceeds the force of friction between the wheels at cart and the ground, then the cart is pushed forward.