That video does not tell you how it is done, although I suspect there is another video that follows that one that does, so perhaps after seeing that one, you will be in a better position to do as you want.
Technically speaking all you need to do is add title="This is a tool-tip" inside an anchor tag like so...
<a href="http://google.com" title="This is a tool-tip. This link takes you to your Google browser" >Google</a>
And this is what it looks like as a simple link.
If you want to associate it with an image you would put an image where the name Google is like so...
<a href="http://google.com" title="This is a tool-tip. This link takes you to your Google browser"><img src="url to image" height="168" width="198" /></a>
Which would look like this...just hover over the image and see the tool tip.
Meaning you can do all this anywhere the text editor is used. But you need to writ the code in the HTML part of the editor
Hope this helps?