What do I need in order to use LaTeX?

In order to use LaTeX on your own computer you will have to install LaTeX itself and an editor. Theoretically it will work with any editor, even under OS X's terminal, if you insist. The easist way (at least that's my opinion) for a beginner is to download and install Gerben Wierda's TeX-fat.dmg plus Richard Koch's TeXShop as the editor. Both have very informative websites, therefore I shall leave it at this.

Get the foundation and program files here and click here to get to the TeXShop website.
Experienced users may wish to have more control over their distribution and should take a look at the Fink project.