Some introductory information about LaTeX
As you may have already discovered, conventional word processing programs such as Microsoft Word are not well-suited to writing documents with extensive formulas and mathematical notation. The standard system used to typeset mathematical documents is TeX and its derivatives, such as LaTeX. You download software to your computer, which can process a document written using LaTeX commands (which are somewhat like HTML commands), and then produce a document in a format such as pdf or ps. This page will contain some basic information and links to where you can get this software, and how you write a basic LaTeX document.
Where to get LaTeX software
Some companies produce commercial TeX installations, but there are plenty of good free open-source installations.
For Windows, one site which hosts a free TeX installation is MiKTeX.
For Mac, you can try MacTeX.
However, these are just distributions which accept some TeX (LaTeX) document and output some other type of file. You still probably want an editor which will let you create LaTeX files in a reasonably organized way. If you wanted to, you could write LaTeX using notepad, but you would have no color highlighting, access to quick macros, and LaTeX-specific help. Fortunately, there are also free editors for TeX. The following suggestions are by no means all-inclusive; feel free to find one you like.
For Windows, TeXnicCenter is one possibility. Terence Tao says he uses this so it has to be at least decent!
For Mac, TeXShop is a possibility.
For those of you with general computer experience, Emacs can also work.
Learning to use LaTeX
Okay, so you've got a LaTeX distribution and a document editor to help you write LaTeX documents. How do you actually write in LaTeX? Many packages have been developed to accommodate the wide variety of needs that all sorts of different users in mathematics, physics, and computer science have in typesetting, but you can learn the basics of LaTeX in a few hours. There are resources available on the Internet as well as books on how to use LaTeX. Again, this list is far from all-inclusive.
On the Internet, you can find links to some documentation at the LaTeX project site.
There are many books written about using LaTeX. One such book is
Of course, a rough and ready way to learn LaTeX is just to look at a sample LaTeX file, look at its output, and then use that as a template to do what you want. Here are a sample LaTeX file (very brief) and sample reference file:
Sample LaTeX file for Math 75,
Sample LaTeX reference file for Math 75.