There aren't that many Dominions fansites. Most of the pages that do exist will be mentioned here before long. The only one I can think of ATM is SunrayBe's site with lots of fan-made documentation, mainly for DomII. It's at
www.freewebs.com/dominions2
EDIT:
I forgot to answer the other question!
There is a tutorial that comes with the game. You probably found it already, if you're reading the manual. Do you mean a game where you can see how more experienced people do things? In that case, this forum has an AAR section which has few AAR that report on the hows and whys of Dominions. The Silent Seas AAR is very good, and actually completed.