All over the internet, including this website, people publish their 3d pictures as “stereo pairs.” These are simply two pictures displayed side-by-side, one to be viewed by your left eye, the other by your right eye. There are two kinds of stereo pairs: “cross-eyed” or “RL,” and “Parallel” or “LR.”
Traditional stereoviews or stereo cards are parallel stereo pairs. They would ordinarily be viewed with a stereoscope of some kind, which helps you to “fuse” the images in your visual field of view, meaning the left eye is focussed on only the left image, and the right eye is only focussed on the right image. This page will teach you how to view a parallel pair in 3d without needing to use a stereoscope. It takes a bit of practice, but once mastered is a very useful skill in the stereoscopic arts.