How can you get 3D from a 2D screen?

A 3D TV or theater screen showing 3D content displays two separate images of the same scene simultaneously, one intended for the viewer’s right eye and one for the left eye. The two full-size images occupy the entire screen and appear intermixed with one another–objects in one image are often repeated or skewed slightly to the left (or right) of corresponding objects in the other–when viewed without the aid of special 3D glasses. When viewers don the glasses, they can perceive these two images as a single 3D image.