The presentation How Sundials Work, which Tony Moss developed for the British Sundial Society website, can be found here.
Many types of sundials have been developed; see this Wikipedia article.
Lots of information on the background of sundial functioning and how to design your own sundial can be found in The Sundial Primer, created by Carl Sabanski of Canada.
Links to all kinds of sundial-related stuff can be found on the Links pages of the British Sundial Society and the North American Sundial Society.