What is Stereogram and stereo-pair?
What is the difference and how do you view them in 3D?
Read the guide here

Here you can see two types of 3D images: Stereo-Pair and Stereogram.

Stereo-pair consists of two identical images side by side but taken from two different angles. Stereogram on the other hand is an automatically dot generated image and it is impossible to see what picture is hidden at the first glance. With a correct eye a 3-dimensional depth will reveal itself from the simple 2-dimensional image. So how do you view these 3D images?

First, a brief description of the focus point.
It is the point where your two eyes locks onto an object to make it look sharp, just like you are now reading this text.

To complicate it a little bit more, there are two different views - Parallel and Cross. To see the parallel 3D images, you must set the focus point "behind" the image.
The easiest way to describe how to look at these 3D images in parallel view is comparable to a mirror. You do not look "on" the mirror to see yourself, instead the focus point unwittingly placed "behind" the mirror. But with the properties of a mirror it reflects the focus point back at you instead. But the principle is the same with these 3D images.

To view large Stereo-Pair images in parallel view is very difficult unless you can squint crazy wide, but on smaller images, it is actually more comfortable than to view in cross view.
To view in cross simply means adding the focus point "in front of" the image.

The cross view method is easier on larger images but it also tires your eyes faster.
For beginners, it is best to write out a simple 3D image and practice it on a piece of paper which is slightly easier than on a monitor.
There is a more detailed guide in English that can be found here.

Practice makes perfect and do not give up the chance with the opportunity to look at images with an extra dimension than the usual two, without any other means.