World of Warcraft is a complex game. There are necessarily a lot of abilities and nuances associated with each class and spec. If we only had three abilities it would be a pretty dull game. The downside of this is that it takes a significant amount of (at least) playtime and probably a lot of extra research to play well.
All this means that a comprehensive guide would end up being more like a user manual. I've been looking into playing a few alts / alt specs recently and it got me thinking of how I first learnt to play my tankadin, and it really wasn't one guide or resource but several. So I thought I'd share a few of my favourites.
This is quite a small community but very friendly and helpful, and usually happy to give helpful answers to even the most specific questions.
This is a much larger tankadin community, with lots of useful information. Probably the best source for theory craft and numbers. This is the home of the Theck after all. The only reason I wouldn't put this as my number one resource is that there is a LOT of information and most of it is aimed at cutting edge progression raiders meaning it can be pretty overwhelming for a beginner.
There are the more general resources of Elitist Jerks, Tank Spot, Wowwiki and wowpedia. These are full of gems of knowledge. But the wikis are a bit out of date, the playerbase is in a bit of a Cataclysm funk I think. And the other two are again quite overwhelming for beginners.