This may not quite be eil5 level, but

You remember old 3d movies with the red and blue images? The way those worked is when you wear the red and blue lens would block one image per eye. So the red lens blocks the blue image, and the blue lens blocks the red image.

This in turn emulates how you actually see in 3d where each eye sees separate images.

Newer 3d movies work on the same principle, but instead of using colors to do it, it actually uses polarities of light. So when you look at the screen without the lenses it looks distorted and blurry because you're seeing 2 images. The glasses block one image per eye depending on the polarity. This allows you to still see all the colors too compared to the red and blue method.