% Include your names at the top.
\documentclass[12pt]{article}

\usepackage{amsthm}
\newtheorem{mytheorem}{Theorem}
\newtheorem{mydef}{Definition}

\oddsidemargin -.10in 
\setlength{\textwidth}{6.6 in} 
\textheight 9.3in 
\topmargin -0.8in

\begin{document}

In the preamble to your latex document, be sure to indicate that we'll
be using the AMS theorem package (the AMS is the American Mathematical Society):
\begin{verbatim}
\usepackage{amsthm}
\newtheorem{mytheorem}{Theorem}
\newtheorem{mydef}{Definition}
\end{verbatim}


\section*{This is the Section Heading}

This is the introduction, where you set up the definitions and the notation for
the  remaining part.  Using the first name in the braces (after \verb|newtheorem|),
we can write definitions and theorems.  Here are two examples.

\begin{mydef}
The derivative of $y=f(x)$ at $x=a$ is defined to be
$$
f'(x)=\lim_{x\rightarrow a}\frac{f(a+h)-f(a)}{h}
$$
if the limit exists.
\label{Deriv}
\end{mydef}

Now in the text, I can refer to Definition \ref{Deriv}.  I can also
refer to the theorem I have listed as well, see Theorem \ref{IVT}.

\begin{mytheorem}
(The Extreme Value Theorem)  Let $f$ be continuous on the closed interval $[a,b]$.
Then $f$ attains a global maximum and a global minimum on $[a,b]$.
\label{IVT}
\end{mytheorem}

And here is how to include a proof:
\begin{proof}
Here is the proof of my theorem.
\end{proof}

The proof environment sets off the beginning with {\it Proof:} and the ending
with a Q.E.D. block.  Here is a numbered equation, and I reference Equation
\ref{EqnLabel1} this way.

\begin{equation}
x=\frac{-b\pm \sqrt{b^2-4ac}}{2a}
\label{EqnLabel1}
\end{equation}

\end{document}

