There is a trick to looking at these - well you can use a special stereoscopic viewer of course. But it is possible to see them as they are without a viewer.
The other way is to hold your finger up in front of the image, look at your finger, and let your eyes go cross-eyed. You see two copies of both the shapes - and want the centre two images to overlap until they coincide. Don't worry if they don't overlap exactly - this is common, depending on your eyesight, and the eye is well able to compensate for small discrepancies in the positions of the images.
Just adjust the position of your finger until they coincide as nearly .as you can make it - and then wait and after a while you may see a shape floating in front of the screen in the middle - with the other two ones to either side still lying flat back in the screen. It will be floating quite a way in front of the screen. . The key actually is to get your finger at the right distance from the screen to match the position of the shape. Now gently move your finger away and mask the shapes to either side with your hands positioned at the same distance as the object - and with a bit of luck, you will see it floating in mid air between your hands :-).
You can make any of the shapes shown on these pages into stereoscopic images in this way.