Here is how to do it:
Create a full screen link for a YouTube Video
Look up the video on YouTube and note the web page address which will look something like this:
Now copy the string of characters after after "v=" (in this case "4rx8RGA2QGg") and put them into an address formatted like this:
In most web browsers and computer set ups this will launch the YouTube video in full screen mode.
Create a full screen auto play link for a YouTube Video
If you want the video to start playing as soon as the link is clicked just add the parameter "&autoplay=1" to the end of the link like this: