We see depth when images from our left and right eyes merge into one; to re-create that in high-def, TVs must refresh the picture at least 120 times a second with alternating frames from the left and right eye, which tricks your brain into only seeing one image. Most new TVs are fast enough to do this, but to be 3-D capable, TVs must include a converter chip and software to break down the signal and separate the left and right images. An infrared of radio beam syncs shutter glasses [below] with the screen to produce the final 3-D effect.
Sony Bravia XBR-60LX900
sonystyle.com

Active-shutter glasses like those included in Panasonic's system, rapidly block one eye at a time so that each eye sees only the frame meant for it. The glasses contain two small, black and clear LCD lenses that darken or lighten when radio or infrared pulse from the TV (or an add-on emitter) signals that the image is changing.
Panasonic Active-Shutter Glasses
panasonic.com

***A Blu-Ray Player is a MUST, when using the above.