\documentclass[11pt]{article}

\begin{document}

Your text here.
%your comment here. 

\end{document}

Note:  anything you write after \end{document} doesn't matter.
Between \begin{document} and \end{document} you may 
insert comments starting each line with a % symbol. 

{article} and its version {amsart} will be the only two 
document classes you will need in this course. {amsart} is a more 
elaborate class designed by the American Mathematical Society 
especially to make math writings easier.  

Try to change [11pt] to [12pt] or [10pt].   
