Read about LaTeX:  http://www.toolscenter.org/about/about-latex

Dowload MiKTeX (for PC) from  http://miktex.org/

Free editors for MiKTeX (Texmaker, TeXnicCenter):

http://www.xm1math.net/texmaker/
Texmaker is a free LaTeX editor, that integrates many tools needed to
develop documents with LaTeX, in just one application.
Texmaker runs on unix, macosx and windows systems and is released
under the GPL license .

http://www.toolscenter.org/
TeXnicCenter is a feature rich integrated development environment
(IDE) for developing LaTeX-documents

on Microsoft Windows (Windows 9x/ME, NT/2000/XP) freely available under GPL.

TeXnicCenter is open source software and available completely free of charge!

LaTeX for MAC:

SAGE - Open Source Mathematics Software: http://www.sagemath.org/.
Mathematica - Technical Computing System: http://www.wolfram.com/.

Links to LaTeX Guides

This is a nice introduction and contains losts of useful commands including bibtex, but does not contain mathematical notation though:

University of Florida, College of Liberal Arts & Sciences

http://web.image.ufl.edu/help/latex/

For mathematics LaTeX Math Symbols:

http://web.ift.uib.no/Fysisk/Teori/KURS/WRK/TeX/symALL.html

Latex maths and graphics:

http://www.eng.cam.ac.uk/help/tpl/textprocessing/latex_maths+pix/latex_maths+pix.html