If your TV has apps and can connect to the Internet, you have a smart TV and most likely won’t need a Roku device. The exception would be some of the first made smart TVs that are not so "smart". But if it is an older television with no Internet connectivity and app download capability, then Roku, Amazon Fire TV Stick or another similar device will come in handy.
Such a device will connect your TV to WiFi and will enable you to watch Netflix, Amazon Prime and a great number of TV channels, all through your Internet connection. You will need to have WiFi in your home, and the TV will need to have an HDMI port. If there is no HDMI port, you can buy a converter.
There are two types of converters, an HDMI to composite converter and an HDMI to component converter. The former is used when the TV has three inputs (two for audio and one for video), and the latter is used when the number of inputs is five (two for audio and three for video). Choose one based on how many inputs your TV has.
Although there are various other devices that can make your older TV “smart”, we mentioned Roku and Fire TV Stick because of their compact size. They can plug in and hide behind your TV without any additional mounting. The Fire TV Stick can even be powered through a TV's USB port, which solves the problem of running an additional cable to the power outlet.
Alternatively to Roku and Fire TV Stick, Apple makes a superior device called Apple TV; however, it is more expensive and less compact than the other two.