Make sure you carefully follow the steps to cast YouTube videos on TV from laptop or pc/Mac :
Step 1: Connect both the devices to the same Wi-Fi network, your computer as well as the TV supporting Chromecast function or connected to a Chromecast device. Some Android TVs come with a built-in Chromecast.
Step 2: Launch the Google Chrome browser on your computer and go to YouTube.com or use the YouTube app in case you have installed it already.
Step 3: Search the video you want to play on the TV, the video will start playing on your laptop. But as we want to play it on the TV, here’s what you have to do. Check the YouTube player, you will see a TV-like icon which is the Cast button, click on it to cast on the TV.
On the YouTube app, the cast button is at the top of the Home screen. while on Chrome, it’s at the bottom-right corner on the player.
Step 4: Click the TV to which you want to cast from the Available devices, tap the Play button to play the video, the video will start playing on the TV.
To stop casting content, tap the Cast button and select Disconnect.
Similarly, you can also cast the whole screen using the Chromecast, all you need is the Chromecast button.