If there are many forces acting on an object how can the force be 0?

The forces are in opposing directions. For example, a car moving on a freeway at

a constant speed applying a certain force forward has a net force of zero because

the force of air friction is equal to the forward force. If the car was accelerating or

braking, the net force would not be zero. Another example: for an object in free

fall at terminal velocity (not accelerating), the force of gravity downwards equals

the force of air resistance upwards. The two forces cancel out and the result is

an even zero.

Another example, easier to grasp . . .

A collegiate tug-of-war. Several members of the football team pulling one end of

the rope north, and the entire Cheerleading squad pulling the other end of the

rope south. The little hankie dangling from the center of the rope is not moving

at all, because the north force and the south force are exactly equal and they

add up to zero. The net external force on the rope is zero, and although there's

some killer tension in it, the rope as a whole remains at rest.