When 2 or more forces cancel their effect?

When two forces cancel each other, they are called balanced forces. Nothing happens when balanced forces are involved. Motion and anything else relating to force can only happen when there are unbalanced forces involved.

If there are two opposite but unequal forces, then there is a net force. The net force is the difference between the two forces, and it acts in the direction of the strongest force. For example, if there are two people pushing on the same box in opposite directions, and one exerts 10 newtons of force, and the other exerts 15 newtons, then the net force will be 5 newtons, and it will be in the direction of the force applied by the person exerting 15 newtons.