The governing LaTeX distribution for Mac OS X is MacTeX. This distribution is actually an all-in-one package as it not only contains the LaTeX distribution, but also several editors and other useful stuff. So let’s cut to the case: head over to the MacTeX website (or here). If you follow the link you can immediately download it. Note that this download is about 2 GB and thus may take a while to be downloaded (depending on your internet connection).
Once you’ve downloaded the distribution, install it by double-clicking the .dmg file. The rest will speak for itself, as the installation procedure is just the same as any other Mac software.
Now, open your Applications folder and search for a folder called TeX. This contains everything you need, as can be seen here. TeXShop and TeXworks are both open source LaTeX editors, released under the GPL. If you want to use one of these, you can start right away. Personally I prefer another editor: Texmaker. It will be shown in the next section how to install this one (which is no rocket science ;)). Furthermore in the TeX folder we see BibDesk, a handy tool for maintaining references for BibTeX. We also see LaTeXit, a great tool that can be used to add LaTeX equations to Powerpoint for instance.
As I said before, you already get two LaTeX editors with the MacTeX installation. However, I’m used to Texmaker so I’ll show you how to install this editor as del (this one is really easy). Head over to the Texmaker website. Next, go to the download section in the menu on the right and download Texmaker. You probably need the 64 bit version, depending on your Mac hardware. Once you downloaded the file, drag and drop it to the Applications folder and your ready to LaTeX!
That’s it? Yes! However, for the control freaks among us there is an extra distribution for MacTeX called MaxTeXtras. You can find it here. This download contains several editors (like Texmaker), utilities, tools and demos you might find handy. Have fun!