I have no idea what a Roku is.

Roku is a little box about 4” by 4” that connects to your TV and wi-fi. It has its own remote control, and allows you to access Amazon, Hulu, Netflix and lots of other viewing sites through your TV. I bought mine about a year ago. It’s $50 and there are no additional monthly fees; although some of the sites that are available through the Roku do charge, you don’t have to use them. It’s great, especially if you use Netflix or Amazon to rent movies.
So if you rent or buy a movie on Amazon or Netflix, you can stream it through the Roku and watch it on your TV, just use the remote that comes with it to access Amazon or Netflix. So you’re not tied to watching it on your PC, or waiting for a DVD to come in the mail.
I am not tech-savvy at all, but I got it set up pretty fast. To access the Roku, all you do is switch the mode on your TV remote from TV to AV and it instantly brings up the Roku menu; then you use the Roku remote to choose the channel, and that’s it.
My sister recommended it to me, and I didn't want to be bothered at first. But it's really easy to set up and use. I like the fact that the Roku remote only has a few buttons, nothing like a TV remote. And it beats watching movies on my PC.