It is cast in five parts. The first four are cast by the individual warriors, and summons the spirit of their totem animals to attack. The fifth is a combination of all four. It summons a very-nifty-looking griffin-like spirit animal, that I guess is supposed to look like all four animals combined.
The Mandala is first seen in episode 13, and the combination part of it is first seen in episode 16. They never actually explain where or when they learned it. It just sort of appears out of nowhere.