Courselets plans to add an editing tool with buttons for inserting equation. Until then, you can simply type your equations using ReStructuredText's built-in LaTeX support. You can type an equation as a separate line as a so-called math directive as follows:
.. math:: c^2=a^2+b^2
Make sure to leave a blank line both before and after any such directive.
You can also include equations within a text paragraph using the so-called math role, as follows, :math:'c^2=a^2+b^2', where the enclosing quote symbols must be the backquote (often the key to the left of the number 1, at the top left of your keyboard).
For more information on writing LaTeX equations, look here: https://www.authorea.com/users/77723/articles/110898-how-to-write-mathematical-equations-expressions-and-symbols-with-latex-a-cheatsheet