They are no different from conventional DVDs except for the fact that the Blu Ray player uses a Blue laser instead of red one to read info off the disc as is done with DVDs now. Blue light has a shorter wavelength and thus you have the ability to store more on a Blu Ray disc as it takes less space for the blue laser to read it.
they are high capacity DVDs that can hold movies in High Definition (HD) because of the size they can hold. you need a blu-ray player 2 play them(or a ps3).