If you like to type in LaTex, simply surround your latex with dollar signs like: $ $ Hello World $ $

But make sure to remove the space between the dollar signs.

$$ \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6\, +\, 6\mathrm{O}_2 \,\rightarrow\, 6\mathrm{CO}_2\, +\, 6\mathrm{H}_2\mathrm{O} $$

Edit by Borek:

Site uses MathJax now. You can use [tеx][/tеx] tags for LaTeX equations, or [itеx][/itеx] for inline LaTeX:

For a polynomial [itex]ax^2 + bx +c = 0[/itex] roots take form

[tex]x_{1,2} = \frac {-b\pm\sqrt\Delta}{2a}[/tex]

where [itex]\Delta=b^2-4ac[/itex].

For formatting of single exponents and indices it is better to use [sup][/sup] and [sub][/sub] tags.