Fly is a damaging Flying-type move that take two turns. On the first turn, the user flies high, avoiding all moves except Gust, Thunder, Twister, Hurricane, Sky Uppercut, and Smack Down, or if the user was targeted with Lock-On or Mind Reader on the previous turn. Gust and Twister will deal double damage, and Smack Down and Gravity will cancel Fly. Fly will fail when Gravity is in effect.
A flying Pokémon does not normally need to know this move for a player to be able to ride and fly on it. Fly can be made a requirement to mount Pokémon by changing the config setting "needHMToRide" to true.