Vaporeon: Use a Water Stone on Eevee
Jolteon: Use a Thunder Stone on Eevee
Flareon: Use a Fire Stone on Eevee
Espeon: Raise Eevee’s friendship, then level it up during the day
Umbreon: Raise Eevee’s friendship, then level it up at night
Leafeon: Use a Leaf Stone on Eevee, or level up near a Moss Rock in games that use location-based evolution
Glaceon: Use an Ice Stone on Eevee, or level up near an Ice Rock in games that use location-based evolution
Sylveon: Raise Eevee’s friendship and know a Fairy-type move, then level it up
Eevee: No evolution method needed