How to include math symbols?

Most of the time you will want an "inline" math equation: the x/2 button above the edit box. You can then put a LaTex command for the symbols you want.
The symbols we will most need are:

LaTeX command	What you get
\geq, \leq	$\geq, \leq$
\times	$\times$
\cup, \cap	$\cup, \cap$
\mathbb{R}, \mathbb{Z}, etc.	$\mathbb{R}, \mathbb{Z}$, etc.
\frac{a}{b}	$\frac{a}{b}$
\alpha, \pi, \theta, etc.	$\alpha, \pi, \theta$, etc.

Here are some other resources: The WikiDot help page on equations (scroll down); the tables of symbols under Producing Mathematical Formulae in LaTeX (David Wilkins). I also created a discussion forum on this page for LaTeX questions and insights.