LCD and LED use the same technology, the difference is the way the picture is illuminated. Old fashioned tube TV's glowed and you viewed the picture. LCD TV's produce a picture that needs a backlight to make it viewable. A standard LCD TV has fluorescent strip lights around the screen to illuminate the picture whereas LED TV's use LED's to illuminate the picture but it's the same type of picture as LCD.

3D TV's allow you to view standard and 3D sources, the latter needs special viewing glasses (obviously one pair per person viewing).

SMART TV's connect to a Network and thus the Internet and allow you to access many different sources of Content such as the BBC iPlayer. Each TV is different so you need to check just what is available from each one. They also allow you to network your TV with a media server which may be your own PC.

I would be surprised if a 3D TV wasn't also a SMART TV.

There are two categories in 3D TV too, which is active and passive. Passive is known for better in terms of viewing experience and better glasses but it's really up to you. but I always tell people not to get active ones, your eye will in pain so much. Most of the 3Ds use active tech now but LG and vizio uses Passive. Hope it helped.