Ok, silly me, it's been years since I've done some HTML classes.
The guide is correct, if you want to write in large font, you have to use the {h3} (Insert Content) {/h3} tags. Except, replace all the { with < or >.
So the code for:
Big Bold Text
is
{h3}Big Bold Text{/h3} except you replace all the { } with < >. Also, only h3 works, none of the other sizes do.