Here's a breakdown:

* Motion: If an object is sliding across a surface, friction acts in the opposite direction of the sliding motion.

* Tendency of Motion: If an object is at rest and a force is trying to move it, friction acts in the opposite direction of the applied force, preventing the object from moving.

Let's consider some examples:

* Pushing a heavy box: When you push a heavy box across the floor, the frictional force acts in the opposite direction to your push, making it harder to move the box.

* Braking a car: When you apply the brakes in a car, the friction between the brake pads and the brake rotors acts in the opposite direction to the car's motion, slowing it down.

* Walking: When you walk, friction between your shoes and the ground allows you to push off and move forward. The friction acts in the opposite direction to the force you exert on the ground.

Important Note: Friction can act in different directions depending on the type of friction. For example, rolling friction acts in the opposite direction of the rolling motion, while fluid friction acts in the opposite direction of the object's motion through the fluid.