You need a Blu-ray player to play Blu-ray discs, same as you need a DVD player to play DVD discs. It's basically that simple.
Blu-ray players are backwards compatible, and will play Blu-ray discs, as well as DVD's and CD's.
Blu-ray discs have Hi-Definition video, DVD's have Standard resolution video, and CD's (VCD - Video CD) have (over-the-air) "broadcast" resolution video.
If you watch an HD-broadcast on your HD TV, it'll look HD. If you watch a regular DVD on your HD TV it'll look like standard TV.
If you watch a HD broadcast on a regular TV, it'll look like regular TV. If you watch a Blu-ray discs on a regular TV, it'll look like regular TV.
If you watch a Blu-ray disc on a HD TV, it'll look like HD, same as an HD broadcast viewed on an HD TV.
The optical disc technologies for DVD (and CD) rely on a red laser to read and write data, the new format uses a blue-violet laser instead, hence the name Blu-ray. The benefit of using a blue-violet laser (405nm) is that it has a shorter wavelength than a red laser (650nm), which makes it possible to focus the laser spot with greater precision. You can pack more data into the same space, giving Blu-ray discs the capability to hold than five times the storage capacity of traditional DVD's, and can hold up to 25GB on a single-layer disc, 50GB on a dual-layer disc, and 100GB on a quad-layer disc. This extra capacity combined with the use of advanced video and audio codecs offers a truly spectacular Hi Definition audio and visual experience.