Polarized glasses are probably the most commonly used in amusement parks and alike. Each lens is polarized at an opposing 45 degree angle.
To display an effect like this requires two projectors. Each projector also has a polarized lens over it, each at opposing 45 degree angles, like the glasses. A polarized lens basically lines up all the light waves so they are in one orientation. These oriented light waves can only pass through a polarized lense that is polarized at the same angle. If the polarization of the lens is different then it wont let that light through. Light coming from the projector oriented at -45 degrees will be seen by one eye, and the light coming from the other projector oriented at +45 degrees will be seen by the other eye. Hence, you can display a stereo pair of images at the same spot and the viewer will see a single 3D image......
When the two images are reflected off screen a mix of light (in both orientations) reaches to 3D glasses, the lenses on the 3D glasses only let the matching polarized light through and the light is split into its separate images before it reaches the users eyes.
Optical equipment like this is expensive, even the glasses can cost up to 3 dollars a piece even when ordered in bulks of 50. The projectors and the lenses cost a lot more. The cost is the main reason why you normally only see polarized 3D at special events and amusement parks.