It's really very simple. 3D works the same way as our eyes. Our eyes are separated by a distance of about 2.5 inches, and because they are separated, we see objects from two different points of view. While 2.5 inches seems quite small, it's good enough to accurately gauge distances as far away as 25 feet.
This image was made with two cameras whose lenses were spaced 2.5 inches apart, just like our eyes. The left image was colored blue-green (cyan) and the right image was colored red before they were combined for 3D viewing.The superimposed images look blurred. But when you put on Deep Vision 3D glasses , the filters in the glasses decode the picture so your left eye sees only what the left camera lens saw and the right eye sees only the right. Your brain combines the images to see true depth and make it seem real. The picture is called an Anaglyph. Move your mouse pointer around the broom to get a better sense of depth.
3D TV and 3D movies are made the same way. Two lenses are used to take the pictures from the same relative position as our eyes. To learn more about 3D stereo movies and 3D TV, visit your local library and look in the photography section. Meanwhile, why not visit our old time 3D Stereo Gallery for a brief look at the world before TV and the web.