On this video tutorial Aaron Nace from Phlearn demonstrates how to use the vanishing point filter in Photoshop to change perspective.
Using perspective correctly will help you create much more realistic composite images. Nace starts this video with an image of a room and he explains what is perspective and how it effects the way we see the room. The purpose of this video is to show you how to use the vanishing point filter to place an image on one of the walls in a realistic sort of way (this sort of demonstration seems to be very popular when explaining perspective apparently).
We have covered different aspects of perspective on Both Photoshop and Lightroom here on LensVid including the great video by Jesús Ramirez: “Using Perspective and Vanishing Point To Create Composites In Photoshop“, Editing & Manipulating Images in Perspective Using Vanishing Point in Photoshop by Bryan O’Neil Hughes, Travel Photography: Correcting Perspective in Lightroom as well as How to Duplicate Anything in Perspective using Photoshop by Nace himself.