This video was very interesting. He talks about embedding content, and styling. First he explains the <del> tag. It basically adds a strikethrough, so as to point out spelling errors. It can be used like this:
<p>I like to <del>to</del> eat ice cream</p>
It would be used if one person was correcting/pointing out spelling errors. Then, he talks a lot about the <img> tag. It is used (of course) to display images on webpages. He also tells about the different attributes (like src=""), and especially the alt="" attribute. If the browser cannot display the image, it replaces the image with the text in the alt="" attribute. Example:
<img src="errorpic.png" alt="This image can't be displayed!">
If the image couldn't be found, or the link was't right it will display the text "This image can't be displayed!". Then, he talks about the <iframe> tag. You can embed content from other sites with it. If you wanted to embed your about page into your home page, you could do this:
He also talks about how Youtube uses this to embed videos into webpages. Before the <iframe> tags, Youtube used a very long string of gibberish, but now it is very much shortened.