Like with any Pokémon game, this story begins with choosing a starter, but your starter isn't a pokémon. It's a main character.
This will be the character the story is centered around. It could be a new trainer ready to take on the Pokémon League, A gym leader trying to get into shape, a side character getting their chance to be in the limelight, or anything in between. The choice is yours, and you have the whole region of Galar to choose from.