First of all you need to set up the page in the header so that you can use as much space as you want - use geometry package like this or similarly:
\usepackage[
total={130mm,277mm},
top=0mm,
bottom=0mm,
left=0mm,
marginparwidth=0mm,
marginparsep=0mm,
centering,
includefoot]{geometry}
Then you need to set small font using \scriptsize and divide your page into three or more columns using minipage environment like this:
\begin{document}
\scriptsize
\begin{minipage}[t]{0.333\textwidth}
~
\end{minipage}
\begin{minipage}[t]{0.333\textwidth}
~
\end{minipage}
\begin{minipage}[t]{0.333\textwidth}
~
\end{minipage}
\end{document}
Then you can use different mathematical environments (use packages mathtools, amsmath, breqn) inside each minipage (where i put ~) like this:
\begin{align*}
&~\smash{c_0 = 1/\sqrt{\varepsilon_0 \mu_0}}\\
&\boxed{
\begin{aligned}
I &= \di e/ \di t\\
\smash{[C]} &= \smash{[As]}\\
\smash{[T]}&=\smash{[Ns/Cm]}
\end{aligned}
}~
\end{align*}
You can use \boxed{} environment to frame the equations. You will need to use \smash{} in order to minimize the vertical spacing of some equations in order not to get too big. Sometimes even \clap{} might come handy - it reduces horizontal spacing.
Inside the align* environment you can vertically align parts of equations with & which will appear one below the other. And you can do this in aligned environment as well.
