Friction works to slow the momentum of a moving object. It acts as an impeding force, to either slow it down or eventually cause the object to stop moving.
There are many examples of friction that provide a practical explanation that is easy to understand. For instance, brakes applied in a moving vehicle will cause friction between the tires and the road, slowing and even stopping the vehicle. The frictional force is enough in this instance to have the grooves in the tires be impacted by the force applied to get them to catch on the road. The friction is applied to the wheels in the opposite direction from which it is moving.