Question: how eevee evolves into leafeon?
Answer: Gen 4's Leafeon and Glaceon have a second Eevee evolution method, by using the Mossy Lure or Glacial Lure respectively. When you're in range of that PokéStop with the Lure enabled, go to your Eevee and choose the Evolution. Meanwhile, Gen 2's Umbreon and Espeon also have a second Eevee evolution method.