Do you want to begin working with the TeX typesetting system? Most people start out by downloading free versions of the needed software, and a tutorial. This page gets you to the most popular choices.
You first need a collection of the software. Such a collection is called a distribution, and comes with TeX, LaTeX, BibTeX, and everything else that will help you to perform TeX's magic on your computer. Each distribution also comes with programs specific to your computer platform, so make your choice from the list below.
Most people starting TeX today use the LaTeX macro package. The most-often recommended tutorial is the (Not So) Short Guide to LaTeX2e; this has many translations. Another tutorial is the Indian TeX group's LaTeX primer.
Many people get a TeX system to write mathematical text. For that, get the documentation for the American Mathematical Society's AMS-LaTeX package.
You might also be interested in a comprehensive list of symbols and a tutorial on graphics.
As a TeX user you will have many resources to help you get your work done.
First, TeX is popular and there are probably many people near you who
have experience with it.
There are plenty of helpful people on the Internet discussion group
comp.text.tex.
And, you are most welcome to join a
users group.
There are many books available. The English FAQ is authoritative, clear, and up to date.
Finally, this site, CTAN, is our community's archive; if you are looking for something then chances are good that we have it.
The TeX Users Group has a more extensive introduction than this page. They also keep the definitive list of all TeX system choices, including commercial options.