Learning TeX (beginning)

This is my first experience with TeX and the document should consist of :

% lines started with % symbol are comments \documentclass[options]{class} % options - mandatory % class - one of the from list (article, letter, report, book, proc, slides) \begin{document} %body of the document \end{document}

An example:

\documentclass[10pt]{article} \begin{document} This is my first \LaTeX document.   Suppose we are given a rectangle with side lengths $(x+1)$ and $(x+3)$ . Than the equation $A=x^2+4x+3$ represents the area of the rectangle.   Suppose we are given a rectangle with side lengths $(x+1)$ and $(x+3)$ . Than the equation $$A=x^2+4x+3$$ represents the area of the rectangle. \end{document}