Latex: font sizes

\tiny
\scriptsize
\footnotesize
\small
\normalsize
\large
\Large
\LARGE
\huge
\Huge
or to change font in larger text part:\begin{small}
something something ...
\end{small}

Double spacing\usepackage{setspace}
\doublespacing
or arbitrary spacing e.g.:\setstretch{2.5}
Two column article:\documentclass[twocolumn,11pt]{article}
In a text, to switch from one to two column use \onecolumn and \twocolumn.
in two-column documents, \begin{figure*} \end{figure*} provides a floating page-wide figure (and \begin{table*} \end{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.