When a person looks at an object in 3 dimensions, he sees the object from different angles. Although the eyes are close enough, if you close one eye then the other, you will see two slightly different images. The brain instantly analyzes the differences between the two images and is able to detect the distance of each object is the viewer, creating our perception of depth. So the key is 3D monitors to display separate images for each eye, simultaneously from cameras installed within inches of each other.
Create images to be displayed to each eye is the simplest part. 3D display drivers can quickly create an image from two different angles in a game. The difficult part is to display the correct image to each eye. The newest breed of monitors games 3d does this polarization of light using.