3D glasses create the illusion of three-dimensional images by showing slightly different images to each eye using colored lenses, like red and blue, allowing the brain to perceive depth. There are different types of 3D glasses like anaglyph, polarized, and pulfrich glasses. 3D glasses are commonly used in movie theaters and for entertainment purposes to view 3D movies and images by feeding different stereoscopic images to each eye to produce a three-dimensional effect, though they can sometimes cause headaches or blurred vision as a negative side effect.