The Perspective Tool is used to change the perspective of the active layer content, of the selection boundaries or of a path. When you click on the image, according to the Preview type you have selected, a rectangular frame or a grid pops up around the selection (or around the whole layer if there is no selection), with a handle on each of the four corners. By moving these handles by click-and-drag, you can modify the perspective. At the same time, a “Transformation informations” pop up, which lets you valid the transformation. At the center of the element, a point lets you move the element by click-and-drag.