What is the difference between dvd and blue-ray disc......?

...also what do you use to play a blue-ray...?

Blue-Ray is a high definition DVD made by Sony. There is a competitor made by Toshiba (I think) called HD-DVD. But it will not have the same fate as Beta.

Play Station 3 plays Blue Ray DVD. And they make Blu-Ray DVD players. If you don't have a HD TV, then you don't need it. You don't NEED it anyways, but it does look really good. And the sound quality is awesome.