Question

What happens when multiple forces act upon an object?

Answer 1

They all combine to affect the object as if there were one single force. It's not hard to calculate the strength and direction of that one equivalent force. It can turn out to be zero. Then the group of several forces is said to be 'balanced'.

Answer 2

The object will move if the forces are unbalanced.

Newtons second tells you that when a net force (the unbalanced force) is applied to and object it will produce an acceleration (movement) in direct proportion to the force and in inverse proportion to the mass of the object.