Plug the Roku box into the wall outlet and your TV. Connect it wirelessly to your WiFi. Switch your tv to the input where you connected your Roku. Set up an account. Then watch whatever content you want.
I stream content from my Netflix account, my Amazon Prime account, and my home video server.
I don’t pay anything to Roku (after the initial hardware purchase) because I’m paying Amazon and Netflix for content. Their content is delivered over the internet to the Roku box and then to your tv.
THX!