|Did you look at the links I provided?|
Smart TVs generally come with a very limited number of channels; some have more, some have less. You didn't state the make/model of your TV so I have no idea what you're working with. I think my 32" Philips smart TV has about a dozen of the most popular channels. My LG smart blu-ray player has only 6 channels. There is no way to add or subtract channels - you get what they give you.
Roku streaming boxes come in several versions (1, 2, 3, or 4) & there's also the Roku stick that plugs directly into the HDMI port. None of them use USB so I don't know what you're asking about in that regard? If you have an older tube type TV with no HDMI port, you can get a Roku 1 which has composite connections (yellow, red, white). It also has HDMI. Like I said, Roku has 1000's of channels. You can pick & choose the ones you want from the channel store & add them to "My Roku". And your "My Roku" can be configured using the Roku remote or you can do it using your PC.
A large number of the Roku channels are free. One of the top freebies is Crackle. It can also be viewed by using a PC or the smart phone app. Did you consider simply connecting your computer to the TV & using it as a giant monitor?