LaTeX is a popular typsetting markup language. For geometry teachers, it allows you to type a series of special commands that can be rendered into proper looking mathematical symbols and fonts.
The Proof Companion already has a group of buttons that allow you to enter common geometric symbols into your proof. If these symbols are sufficient for you, there's no need to use LaTeX at all! If you want to use more advanced notation (i.e. fractions, exponents, segment and ray notation, etc.), you'll need LaTeX code.
Inside the text boxes where you enter statements and reasons, simply include valid LaTeX in between double dollar signs. For example, if you type: $$ \overline{AB} $$, it will render as when you generate the proof.
$$ a^2 + b^2= c^2 $$
$$ \frac{1}{2}\angle{A} $$
$$ \theta = 35^\circ $$
$$ \overline{AB} + \overline{BC} = \overline{AC} $$
x^2, x^3, x^4
Angles:
\angle ABC > \angle EFG
Fractions:
\frac{2}{3}
\frac{2x + 1}{3}
Symbols:
\pi, \theta, \parallel, \perp, \cong, \sim
Notation:
\overline{EF}, \overrightarrow{GH}