LED,LCD and Plasma, Whats the difference?

So I just started a job at Sears in the electronics department and I need a little help. I don’t understand the difference in all of the TV’s except for Plasma, I know its a liquid and its framed in glass but other then that not much.

If someone would be able to explain it easily for me I’d really appreciate it.

No, they don’t teach you any of this on training.