Beamer is the class that deals with presentations. Go to beamer to learn more.
Pour JAC:
Open a file “my\_own\_notations.sty”
%% some stuff ...
% get home variable
\def\newtemp{}%
\newcommand{\getenv}[2][]{%
\CatchFileEdef{\temp}{"|kpsewhich --var-value #2"}{}%
\StrGobbleRight{\temp}{1}[\newtemp]% Delete the trailing whitespace character
\if\relax\detokenize{#1}\relax\temp\else\edef#1{\newtemp}\fi%
}%
%========================================
%partial derivatives
\newcommand{\pade}[2]{\frac{\partial #1}{\partial #2}}
%% some other stuff ...
Put this file in a folder “texmf/tex/latex/local/my\_own\_notations.sty”.
You you shell rc (~/.bashrc , ~/.zshrc , etc), export this path:
export TEXMFHOME=path to the previous folder/texmf
Now you can use it as any other package.