Reddit reviews The LaTeX Companions Third Revised Boxed Set: A Complete Guide and Reference for Preparing, Illustrating and Publishing Technical Documents (2nd Edition)

>Additionally, do you know a good site to teach me how to use LaTex like this.

For awhile, the joke about LaTeX vs. Microsoft Word was that while LaTeX was free, the references you needed to buy to learn LaTeX meant the total costs were roughly equal. To that end, I've found this collection of reference books invaluable.

If you'd rather save ~US$160, though, then I'd say that the best way to learn LaTeX is to practice LaTeX: if you see something in a textbook, then try to figure out how to write LaTeX code that would reproduce that. Simpler documents can be mostly straightforward, but anything with graphs of functions or commutative diagrams may require more detailed understanding of how to generate graphics within LaTeX or how to import graphics produced via other means.

Oh, and many people make their LaTeX source code available one way or the other, so you can learn how someone else did something by stealing borrowing their techniques. On reddit, for example, hit the "source" button under one of my comments, for example, and you'll see what I typed so that reddit (via your plugin) displays those particular formulas and expressions.

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Addendum: I should have mentioned that the full power of LaTeX isn't really apparent within reddit alone. If you want to do anything from automatic equation-numbering to LaTeX-native graphics, you'd want to work with a LaTeX distribution on your own, ideally with a front-end editor/compiler, too.