"Device" just means the screen where you're gonna watch. Could be a phone, tablet, Apple TV, Roku, or computer.
Click on this site. Let me know if you see an animation or a screen that tells you to download silverlight. http://bubblemark.com/silverlight2.html
I have pretty severe ADD and I rarely read threads all the way through - in fact, I think this is the first time I do it. I hope you get this figured out. What is the EXACT message that you get when you try to sign in?