A stereoscopic picture is one which has depth to it; true 3 dimensions.
The subject of the photo should be a stationary (non-moving) object. Note that these pictures are almost identical. The idea is to have your left eye focus on one pic and your right eye on the other. You should be able to stare at this set of pictures and see the depth, the "stereo" effect. The centers of the pictures should be roughly the same distance apart as the centers of your eyes.
Set your camera up on a tripod and focus on a point in the scene. Take the picture. Take particular note of the exact center of the pic. Be careful that you do not move too much or "turn" instead of "sliding" sideways. The idea is to take each picture the way your eyes would see the scene. One picture for each eye.
If you are not in a position to take digital pictures right now, you can right-click on the photos in this website, save them and use them.
Move the tripod to the right so that the center of the camera lens is 5 inches (13 cm) to the right of where it was. Make sure the camera is pointed at the exact same spot where it was pointed for the first picture and take picture number 2. My son David suggested: "For close objects (less than 30 feet) I would put the camera only about 4 inches apart between shots. For outdoor, long distance shots, I would put them about a foot apart. It exaggerates the effect, but that's kinda the point."
Load the 2 pictures from your digital camera into your computer; possibly making a special new folder in which to save them, and save them as, e.g. "dogleft.jpg" and "dogrite.jpg" and then resize both to whatever size your viewer can handle; I used 190x143 pixels.
For me, 300x225 works OK also. Cropping is not a good idea.
Print the pictures with a small space between them. You may need to experiment with the width of that space.
Here are two pictures of my Diamond Willow sticks, UNfinished; note the depth!
You can see the stereoscopic effect but to make it easier, you can make a viewer out of cardboard and tape.
Here is the viewer I made; crude but effective.
Note the rounded notch for your nose.
Following are the pieces of cardboard I used to make my viewer. Note that on the end of the box nearest your face, the top part, you might curve the part that sits against your forehead, and cut a notch in the bottom for your nose. When you glue the "END PART" on, leave 1/2 cm or so for a slot to slide the pictures in. These pictures are not to scale. When I put mine together, I put a bead of carpenters glue on the edges of the sides before setting them on the bottom and setting the top onto the sided. Don't forget to set the "divider" into the slots before gluing the sides and top/bottom together.
Here is another viewer you can make. The part with the notch for your nose slides in and out so you can adjust the distance from the picture to your eyes.
Here is one more I did, of my cabin where I find my Diamond Willow sticks.