How is it done?
This site supports the LaTeX syntax and rendering through the MathJax engine.
You can use the normal LaTeX syntax, but you have to enclose the formulas in
$$ tags for centered formulas,
\$ tags for inline formulas.
There is a sandbox here, where you can find several examples.
<sup> tags would do the job too
I2Rload is produced by
In the case of superscript-2, you can also use the native HTML "²" construct, like
P = I² R