the currently recommended way

We're mostly using the http://www.mathjax.org/ approach now - check there for the documentation. The gist is tat all these pages load a javascript library in the header, namely http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML , which automatically renders AMS LaTeX into a web-compatible form.
Just put your LaTeX between backslash parens (e.g. \ ( ... \ ) for inline math) or backslash square brackets (e.g. \ [ ... \ ] for separate line) without a space after the backslash.
Here an inline example : $$\frac{\alpha}{1+\infty}$$.
And here's a separate line example :
$\int_0^1 sin(x) \, dx$
Indented (codeblock) lines do not go through the MathJax engine, so the source for the formulas above look like this.
 $$\frac{\alpha}{1+\infty}$$ $\int_0^1 sin(x) \, dx$ 

the old way

testing the < math > tag

Some formulas are displayed with HTML. (The top line has extra spaces in the math tag to keep it from doing its thing and leave TeX is visible.)
 < math > y = \gamma + \beta < /math > y = γ + β 
Others will display with a png image. In either case, the software should do the right thing automatically.
 < math >x = \frac{-b \pm \sqrt{b^2 - 4ca}}{2a}< /math > 
If you'd like to force the png image version, perhaps because you don't like the way the html formatting looks, you can put the word "img" within the first math tag, e.g.
 < math img > y = \gamma + \beta < /math > 

other ways

There are a few other ways to input other characters, too: HTML special symbols (e.g. "& alpha ;" without the spaces and utf-8 characters. How this shows up for you will depend on your browser and available fonts.
Here's the lowercase greek alphabet in utf-8 character.
(I used the Mac "Show Keyboard Palette" under "Keyboard" to type the characters.)

α β γ δ ε ζ η θ ι κλ μ ν ξο π ρ σ ς τ υ φ χ ψ ωϑ ϒ ϕ ϖ
Or using HTML symbols (e.g. "& alpha ;" without the spaces).
α β γ ...
or within individual math tags
α β γ ...
or all in one tag
αβγ

 1 α + γ

1

 1 1 + 1 + 1
Is it true that ?

More testing.
sin(x) / x = f(x)
 sin(x) = f(x) x

pre-superscript for sam ... using a "negative small space, positive small space" trick.
 
 1 2 
http://cs.marlboro.edu/ courses/ marlboro_wiki/ math_on_wiki_pages