Spin causes the sideways action of the ball after it has hit the ground.
Swing is where you shine one side of the ball in order to reduce the air resistance on that side, thus making the air movement around it smoother. This has an effect of making the ball curve in the air.
So swinging a ball isn't much different from normal bowling, but with a spin on a ball the motion as it's released from the hand has to be different, so yes it's an individual skill in itself.