Here is a page discussing how to write mathematical expressions in LaTeX:
http://en.wikibooks.org/wiki/LaTeX
http://www.math.umbc.edu/~rouben/beamer/ A Beamer tutorial
http://www.andy-roberts.net/misc/latex/ LaTeX tutorial
http://www.ams.jhu.edu/~ers/learn-latex/ Another LaTeX tutorial
http://www.tug.org/texworks/ TeX installation for Macs and PCs
http://pages.uoregon.edu/koch/texshop/ TeX installation for Macs
http://miktex.org/ TeX installation for PCs
Here are some links recommended by Samantha Youmans:
http://www.latex-project.org
http://amath.colorado.edu/documentation/LaTeX/Symbols.pdf
http://deic.uab.es/~iblanes/beamer_gallery/index_by_theme.html