\documentclass[12pt]{article}
\usepackage{graphicx}
\usepackage{amsmath}

%  A "comment" starts with a percentage sign- They are ignored by LaTeX

%These are some "nice" values- You can change them to your own tastes:
\oddsidemargin -.10in 
\setlength{\textwidth}{6.6 in} 
\textheight 9.3in 
\topmargin -0.8in

%This is how you can define your own LaTeX commands- In this case, 
%  if I type \R I will get the symbol for the real numbers (there are other alternatives as well}

\def\R{{\mathchoice{\rm I\hskip-.2em R}{\rm I\hskip-.2em R}
    {\rm I\hskip-.15em R}{\rm I\hskip-.1em R}}}

\title{This is a title}
\author{These are, the authors, separated by commas}

\begin{document}

\maketitle

This is a document....

\end{document}
