microsoft silver light, why do you need this on a mac?

[UCLA Bruins Fan]

So I got sighted assistance, and silver light is now installed on my  
mac.  Once it was installed the stream loaded fine, but I am curious  
about why I needed to install this in the first place? Also, is there  
a way this could have been done with out sighted help?
I was unable to interact correctly with the page on safari despite  
trying numerious times.
Olivia
GO BRUINS!!!!:)