The TV should be HD as in something newer with the HDMI input for the Roku, Amazon Fire TV, Apple TV or other box to connect to. You'll need a good to excellent internet connection.

http://www.cnet.com/topics/media-streamers/best-media-streamers/

Nod to the Roku 3 and my pick is the new Amazon Fire TV (if you have Amazon Prime, a lot of free content there.)