http://www-h.eng.cam.ac.uk/help/tpl/textprocessing/columns.html
Most classes take a [twocolumn] option command switches to single column output and the \twcolumn command switches back, but both commands start a new page.
Putting page-wide items into a two column document can pose problems
Figures and tables - See the FAQ entry. http://www.tex.ac.uk/cgi-bin/texfaq2html?label=widefigs
There are alternative versions of the float environments - in two-column documents, figure* provides a floating page-wide figure (and table* a page-wide table). The "*"ed float environments can only appear at the top of a page, or on a whole page - h or b float placement directives are simply ignored.
Unfortunately, page-wide equations can only be accommodated inside float environments. You could include them in figure environments, or use the float or ccaption package to define a new float type.
In twocolumn mode, \newpage and \pagebreak start a new column whereas \clearpage and \cleardoublepage always start new pages.
In a twocolumn document, the ftnright package puts footnotes only under the right columns.
The multicol package lets you change the number of columns in mid-page and its effect can extend over several pages. The columns on the final page are balanced (equal height) by default.
Here's an example of getting 3-column output.
\begin{multicols}{3}{ Put the text here. Maths, tabulars, pictures etc are all ok (but not figures and tables). Remember to load in the \texttt{multicol} package at the top of your document. } \end{multicols}
Figures present a problem in a multicol environment. See the multicol hints page for details. http://www-h.eng.cam.ac.uk/help/tpl/textprocessing/multicol_hint.html
See the LaTeX FAQ. http://www.tex.ac.uk/cgi-bin/texfaq2html?label=balance