Three different styles have to be distinguished when creating multiple columns in a Latex document. Either we want the whole document to have two columns, single pages or only part of a page. In order to do so, three different Latex commands are used…
Whole document (using article to write a paper):
The only thing you need to do is changing the first command of your Latex-file.
\documentclass[11pt,twocolumn]{article}
It will automatically create two columns in the entire document.
Note: if you are writing a paper, IEEE provides useful templates which can be used and adapted to your needs. You can download them from their “Author Center“.
Single pages:
The command \twocolumn starts a new page having two columns. Accordingly, \onecolumn starts a new page with a single column assuming you are in a two column environment as described above. Both commans do not take any arguments.
The is a way to define the distance between the two columns, use
\setlength{\columnsep}{distance}
If you need a line to separate the columns, the following command will do the job:
\setlength{\columnseprule}{thickness}
Part of a page:
I have posted another article on that, just have a look there. \minipage can also be used for text, not only for figures and tables.