There are several ways to do this, including the following:
If you have an Apple computer or mobile device and an older Apple TV, you can use AirPlay to see the videos on your TV.
If you have a Google Chromecast device, you can cast (send) video to your TV from a Chrome browser. While playing a video on your computer or device, click the Cast icon.
You may be able to connect your computer, tablet, or smartphone to your TV using an HDMI, DVI, VGA, or S-Video connection. Consult the manuals for your computer or mobile device and your TV to find the best option.