why are wedges and screw types of inclined planes?

Answer 1

A wedge is clearly an inclined plane. If you move it horizontally, an object that is constrained not to move horizontally and slides on the wedge moves vertically. The lower the slope of the wedge the greater the force advantage the wedge provides.
A screw thread is just a wedge or inclined plane wrapped around a cylinder, so a rotary motion of a screw provides the same kind of multiplication of effort that the wedge does.