Stereoscopy, or Stereoscopic 3D, is a way to create the illusion of depth from two flat images photographed or drawn at slightly different angles. It simulates what happens every waking moment of our life when our brain fuses the two flat perspectives seen by each of our eyes into a unique three-dimensional mental picture. Whatever the technique used to view stereoscopic pictures (lenses, prisms, mirrors, glasses, filters, etc.), the idea is that the left eye can only see the left image and the right eye the right one, thus feeding the brain with the two separate inputs needed to operate the fusion into a three-dimensional representation.
For help with viewing stereo images, please see this link.
For help with taking stereo photos, please see this link.
If you would like to learn more about the first 30 years of stereoscopy, please refer to the London Stereoscopic Company’s book ‘Stereoscopy: The Dawn of 3D’ https://shop.londonstereo.com/stereoscopy-the-dawn-of-3-d.html