Vista - Silverlight? What is it?

Every time I search Microsoft for information I come across Sliverlight;
download Silverlight here...

OKay, so I did. Nothing! From what I understood it is a richer alternative
to flash player. I love watching movies on the internet. But nothing
changed. Either the flash player or Move player continued to be used.

I am aware I probably did not configure it properly. So before I go on
another download adventure, will someone please explain what exactly is
Silverlight; and if time permits, how do I configure it and is it worth it?

Thank you,

Nissi1