Cords often include content, which is why they cost money (besides the installation and maintenance of the cord.)
There are thousands of channels on Roku. Some are "cable channels" that are available for use in alternate situations. Some like Netflix and Amazon are premium channels that you pay directly. Some are completely free (usually advertising supported, sometimes donation supported). Some content providers have multiple ways of letting you pay. For example, with something like HBO, you might be able to use your cable company provider or pay them directly if you don't have a cable company.
There are also things like slingTV which are kind of a virtual cable subscription.
I would guess that many if not most Roku owners do in fact have cable or satellite TV and use the Roku to add things like Netflix and Amazon.
