By default, all Pokémon have two attacking moves: a Fast Attack and a Charged Attack. Fast Attacks deal a small amount of damage, while also powering up a Charged Attack. Charged Attacks can be used once they’re fully powered up and they also deal larger amounts of damage. You can teach your Pokémon another Charged Attack by exchanging Stardust and Candy. Once learned, it will also be available to use in Raids, Gyms, and Trainer Battles. This option is accessible in the Pokémon summary page. 
Additionally, some Charged Attacks have extra boosts or drops. These are represented on the Pokémon summary page as well. When these Charged Attacks are used in Trainer Battles or Battle Training, they have a chance of activating the boosts or drops. 
Using TMs
Additionally, you can use Technical Machines (TMs) to make a Pokémon forget an attack and learn a different one in its place. Fast TM Teaches the Pokémon a new Fast Attack 
Charged TM Teaches the Pokémon a new Charged Attack 
_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-
Pokémon GO Game GUIDE