Linux' applications are very well documented in my opinion.
I've always found that, provided I have the skill, man pages and official HTML doc are the best way to get me to where I want.
As someone said above, all things are explained in man pages, but it often doesn't say why you'd want to use those things. So forums are often usefull to get helped on the basics first. When you know more on your subject, then man pages and full HTML references are a great wealth of information.