To get a computer's video output to go to a television, hook it up to the television via an HDMI cable, or use Google Chromecast. Alternatively, you can use Apple Airplay if you have an Apple TV box.
The easiest way to view a computer's display on a television is to connect both devices with an HDMI cable. Simply plug one end of the cable into the HDMI port of the television and the other end into the HDMI port of the desktop or laptop. Then, change the input of the television to the corresponding HDMI port. If the computer doesn't have an HDMI port, you can purchase an adapter. For example, Apple's MacBooks require a Mini DisplayPort to HDMI adapter cable.
Google Chromecast sends the contents of an app or webpage to a television. It also contains an experimental feature that displays the whole desktop screen on the television. Results of using Chromecast vary depending on how strong the Wi-Fi connection is and how powerful the computer is.
If an Apple TV box is present, you can use Apple Airplay to display the contents of a Mac, iPad or iPhone on the television. AirPlay wirelessly mirrors an Apple device's contents to the screen.