Hey Jeanne, I'm Tim. Silverlight is a plug in, kind of like flash or java.
Its usually used to play videos.......its being phased out with java and flash since HTNMl5 is out, and most sites or what ever are just using htnl5.
good question. im sure you have heard of html, its what web sights are written in, and have been for a long time, however normal HTML can't do smart stuff, like play a video, or a song - they need plugins, like Java, flash, silverlight.......HTML5 has been out a while, and its inbeded in the new browsers, so no plug ins are needed for content.....thats the idea anyway, at somepoint everyone has coded in HTML5. and then all these plug ins can go away.
you JUST asked me what html5 IS.
Just download it and install it, it should run no problem unless your on a tablet or something.
if you like i can remote in and install it for you.
what do you mean by online files? if its asking for silverlight, thats the plug in it needs.