You can't.
You get Squirtle as one of the starter pokemon.
You can only obtain squirtle as your starter pokemon( your first pokemon) or through trade.
the starter Pokemon are charmander, bulbasaur, and squirtle.
bulbasaur, squirtle and charmander
firered and leafgreen version
you have to get squirtle as your starter
you can't, you need to trade with a game that you can start with a squirtle (ie. Pokemon leafgreen, Pokemon firered)
You start off with Bulbasaur, Squirtle, and Charmander. You start off with Bulbasaur, Squirtle, and Charmander.
You cant catch a squirtle in Pokemon firered nor in Pokemon leafgreen. Squirtle is a starter Pokemon so you cant find or catch one unless you use a game shark.EDIT by Man spider27: Although it is- as far as I know- impossible to capture Squirtle or Bulbasaur in Pokemon leafgreen it is possible to find Charmander in the Old Mansion on Cinnabar island. Hope I helped!
you have to migrate from leafgreen/firered from squirtle
only if you had a gameshark or if it was your starter
choose squirtle as your starter then evolve it.