Help:LaTeXMath
1 What is LaTeX?
LaTeX is a markup language, like HTML and wiki markup. It's very handy for describing and displaying math formulas.
2 Getting Started
All wiki LaTeX expressions lie between <math>
and </math>
tags. Let's start with simple examples and work our way up.
Description  You type  You get 

LaTeX makes numbers and symbols look prettier.
Letters are italicized to look like variables. 
<math>y = x  2z + 13</math>


^ for exponents

<math>y^2 = x^3  486662x + x</math>


LaTeX is quite dumb, it treats adjacent symbols separately, rather than as a single term.  <math>y^2n</math>


Use curly braces to group them together  <math>y^{2n}</math>

3 Easy ways to learn how to write math using LaTeX
The easiest way to learn LaTeX math is to look at how other people write it. The "source code" for documents prepared using LaTeX usually end in .tex. These are plaintext files that can be read in any text editor. You can also see how other people write it in the wiki by clicking on the Edit Page tab.
Mathematical expressions in .tex files don't lie between <math>
and </math>
tags. Instead, they may look like
$ O(n \log n) $
$$ \gcd(a, b) = 1 $$
\begin{align*} x^2 & > 0 \\ x & \neq 0 \end{align*}
Remember to convert to the correct tags. In the last example, & and \\ are alignment and newline operators and should also be removed when converting to wiki LaTeX.
4 Commonly Used Commands
Description  You type  You get 

Fractions  \frac{n}{2}


Large delimiters  (\frac{n}{2})


Floor and Ceiling  \Bigl \lfloor \frac{n}{2} \Bigr \rfloor


Summation  \sum_{i=1}^n i^3 = (\sum_{i=1}^n i)^2

For more commands, check out the excellent Short Math Guide for Latex by Michael Downes.