Although looks complicated at first sight, done once you will realise how easy it is and how worthwhile it is for maximum enjoyment

From Mobile phone:
Make sure it is connected to the same wi-fi network as your TV
You will need to link your phone to your TV. The method will vary from phone to phone and whether you have an Android or Iphone
Some phones come with chromecast which makes it easier.
Otherwise
1. On your TV. Launch YouTube
2. On your phone open YouTube app and click on blue initial top right then ‘settings’
3. On your phone click on ‘Watch on TV’ and with any luck you will see your TV on the list to choose
3a Otherwise:- On your TV navigate to settings and select ‘Link TV and Phone ‘ and you will get an 8 figure code
On your Phone enter the blue 8 figure TV code shown on your TV screen into the box. ADD THIS TV.

From PC or laptop
Make sure that it is connected to the same network as your TV
Using Chrome as your browser makes it slightly easier but others will work
1. On your TV Launch Youtube
2. On your TV navigate to settings in YouTube and select ‘Link TV and computer ‘ and you will get an 8 figure code (Make a note of it)
3. On your computer use browser to connect to www.YouTube.com.
4. On your computer make sure you are logged into to your google/gmail account
5. On your computer Click on blue initial at top left and choose settings and then ‘Watch on TV’
6. On your computer enter the blue 8 figure TV code shown on your TV screen(from 2 above) into the box. ADD THIS TV.

On either Mobile or computer launch the video from the link. Pause the video if necessary and look for the Cast icon
(rectangle with arcs of a circle radiating from bottom left hand corner) which will switch the presentation to your TV
To stop casting content, tap the Cast button and then Disconnect.

Note: if you are using the blue code to connect mobile/computer to TV you will need to get a new code each time as the code changes