For some courses I take, we are allowed to write a summary and to used it at the exam. The summary allowed is usually limited to something like ten A4 pages. I quickly googled for latex templatex, but I couldn't find anything useful so far.
The template should allow to used the full space available on an A4 paper, by default latex documents usually have large borders. I guess I'm not the first person looking for this kind of template, so please post any links if you know good templates.
You can setup your margins pretty easily using the geometry package (which should be part of most latex distributions I believe) http://ctan.org/tex-archive/macros/latex/contrib/geometry/
You 'll probably also need one of the multiple column layouts and ams math packages.
You can find a bunch of details on page layout here http://en.wikibooks.org/wiki/LaTeX/Page_Layout
I'd probably use something like this:
\documentclass[a4paper]{article}
\usepackage[margin=1cm]{geomtry}
\usepackage{amspath}
\usepackage{multicol}
\begin{document}
\begin{multicols}{3}
... MY STUFF HERE ...
\end{multicols}
\end{document}
EDIT: Original version was trying to use the plain style, which seems to not exist. Also had the usepackages inside the document rather than the preamble, and had some spelling mistakes. Wont look useful until you fill it with some stub data ... google for "lorem ipsum" to get random filler text.