Here's a sample document that I've written before, which should give you the feel for how this works; its a little bit different than how you would do things on MHF. XD

Code:

\documentclass{article} %book, amsbook, amsart, exam, beamer, etc.
\usepackage{amsmath,amssymb,color}
\begin{document}
\begin{flushleft} % left justification; right justificiation - flushright; centered - center;
Here is first line \\
{\color{red}Here is second line.}\\
Here is third line.\vskip1in
{\color{blue}Here is fourth line.}\vskip1pc
\end{flushleft}
Onto some math forumulas...\vskip1pc
Green's Theorem: $\displaystyle\oint f(x,y)\,dx+g(x,y)\,dy=\iint\limits_R\left(\frac{\partial g}{\partial x}-\frac{\partial f}{\partial y}\right)\,dA$.
Gamma Function: $\Gamma(x)=\displaystyle\int_0^{\infty}e^{-t}t^{x-1}\,dt$
Some symbols...
\[\forall,\,\exists,\,\in,\,\cup,\,\cap,\,\wedge,\,\vee,\,\neg,\,\ldots\]
System of Differential Equations
\[\begin{aligned}
\frac{dx}{dt} &= x^2+t^2 \\
\frac{dy}{dt} &= 2y+\ln t+xyt
\end{aligned}\]
\end{document}

Hope this helps!

**EDIT**: And FYI - the '%' symbols represent the start of a comment. If you want % to appear with the text in your compiled document, you would need to use the command '\%'.