If you're new to LaTeX, you should start with the Guides. If you're already familiar with LaTeX, you're probably just here for the templates, which are available in the sidebar.
The LaTeX Wikibook is an excellent (and very thorough!) guide to many features of LaTeX, ranging from the most basic commands to extremely advanced techniques. Highly recommended.
Stack Exchange is a network of sites where users can ask and answer questions. The TeX-LaTeX Stack Exchange is a great resource for finding answers to both common and esoteric questions—but be careful! Not every answer is good!
A search engine is an invaluable resource for learning any new technology. Not sure how to typeset an integral? Baffled by a cryptic error message? Just Google it!