LaTeX has established itself as the most widely used specialist Mathematical typesetting language, and learning at least the basic will be very useful for anyone considering studying Mathematics at a higher level. All of the documents in the Work and Puzzles section of this site are written in LaTeX. I have listed here some basic links to get you started.|
LaTeX Project homepage - Has all the basic documentation to get you started (read the Not-So-Short Introduction at least once!) and details on where to get the software.
LaTeX Community Forums - I haven't used this extensively, but it looks like it could be useful for troubleshooting/advice.