On my website, to insert mathematics you have to use LATEX. For instance, let's say we wish to insert math within a sentence such as $q_{\rm rad}$ is equal to $\epsilon A \sigma T^4$. This can be done by typing \$q_{\rm rad}\$ is equal to \$\epsilon A \sigma T^4\$. Or, if you wish to display an equation by itself out of a sentence such as: $$ q=-\frac{\Delta T}{\sum R} $$ The latter can be accomplished by typing

$$ q=-\frac{\Delta T}{\sum R} $$

Greek symbols are generally written the way they are pronounced. Thus, $\theta$, $\xi$, $\psi$ can be written as \$\theta\$, \$\xi\$, and \$\psi\$ respectively. Capital Greek letters are written by uppercasing the first letter. Thus, $\Psi$, $\Theta$, and $\Xi$ are typeset as \$\Psi\$, \$\Theta\$, and \$\Xi\$. If you wish to write an equation with an equation number as follows: $$ \begin{equation} F=ma \tag{23a} \end{equation} $$ The latter can be typeset as