Catch an Eevee
Collect 25 Eevee Candy
Set Eevee as your buddy
Walk 10 km with Eevee as your buddy
Keep Eevee as your buddy
Evolve Eevee during daytime or nighttime while near a PokéStop with a Glacial Lure Module to get Glaceon
If the evolve button shows Glaceon, you can evolve it directly while the Glacial Lure Module is active
Use the nickname trick once by renaming Eevee to Rea before evolving to get Glaceon instantly