It belongs to the same family of solitaire games as Strategy, Sir Tommy, Calculation, and Puss in the Corner.
Game-play is like Sir Tommy, but with two decks, a fifth waste pile, and a Canfield-like reserve (referred to as the 'Frog').
Once the reserve is formed, it is then squared up (i. e. arranged to become one neat pile) and placed face up.
As in the other games mentioned above, it is a good idea to reserve a wastepile for both kings and queens and to build downwards whenever possible in order to win.
Fly is a solitaire card game which is played the same way as Frog.