When an object is in equilibrium (either at rest or moving with constant velocity), the net force acting on it zero. A vector can only have zero magnitude if all of its components are zero.

What happens when the net force is equal to zero?

His First Law states that an object with a net force of zero acting on it will remain at rest, if initially at rest, or it will maintain a constant velocity. Whenever a spring is stretched, if it is to remain motionless, it must experience equal and opposite forces at either end.

Will the net force be equal to zero if the force is unbalanced?

If the forces are unbalanced forces, the effects don't cancel each other. Any time the forces acting on an object are unbalanced, the net force is not zero, and the motion of the object changes.