These pages are about XML schemas - meta-language for describing the structure of XML documents and validating them. Naturally, there are all sorts of other pages around that cover schemas for XML. Jeni's Schema Pages are dedicated to helping people understand and make the most of using schema languages.
These slides are from the XML Schema tutorial that I gave at Extreme Markup Languages in 2002 and yes, I'm afraid that they were created using PowerPoint. You can download everything, or just the exercises, as zips:
Or browse through the HTML (IE only):