To view STEREO PAIRS by the CROSSED eyes method:

It may help to position a fingertip or the end of a pencil between your eyes and the images, about one-third of the way to the screen. Focussing on your finger, slowly shift your attention to the images on the screen. When your right eye sees the left-hand image and vice-versa, the images will appear to overlap in the center to form the 3D stereographic illusion. You will know it when you've got it.

<
. . .