This article explains how to change the perspective of a photograph. After opening the image in photoshop, you go to edit and then click perspective warp. You then draw the edges of the quad. After doing that, you switch from warp to layout mode and are able to move the quads you set around to change the perspective. This is important if you shot an image of a building or something similar and want to change the angle of the photograph.
https://helpx.adobe.com/photoshop/using/perspective-warp.html