Distort allows you to move one corner of an element, independently of the other 3 corners.
When an element (most element types are supported) is selected, the Distort option becomes available. Selecting it will do two things, first it will convert that element to a Pen element. Second, it will bring up the distortion frame which has a control point on each corner of the element. You can move any one of these control points and the entire element will stretch to fill the new bounds you create.