What does dogen's genjo-koan mean? What does the genjo-koan means? Especially:


  To study the buddha way is to study the self. To study the self is to
  forget the self. To forget the self is to be actualized by myriad
  things. When actualized by myriad things, your body and mind as well
  as the bodies and minds of others drop away. No trace of realization
  remains, and this no-trace continues endlessly.


and


  A fish swims in the ocean, and no matter how far it swims there is no
  end to the water. A bird flies in the sky, and no matter how far it
  flies there is no end to the air. However, the fish and the bird have
  never left their elements. When their activity is large their field is
  large. When their need is small their field is small. Thus, each of
  them totally covers its full range, and each of them totally
  experiences its realm. If the bird leaves the air it will die at once.
  If the fish leaves the water it will die at once.
  
  Know that water is life and air is life. The bird is life and the fish
  is life. Life must be the bird and life must be the fish.
  
  It is possible to illustrate this with more analogies. Practice, enlightenment, and people are like thi


What does it mean to say that these are life and that there's no realisation?
Dogen is pointing to emptiness. When the self drops, you realise you are one with the ten thousand things, and there is no more I and them. Enlightenment, path, etc are no more than concepts.

The Heart Sutra:


  "Shariputra, form does not differ from emptiness, emptiness does not
  differ from form. That which is form is emptiness, that which is
  emptiness form. The same is true of feelings, perceptions, impulses,
  consciousness. "


And:


  "Therefore, in emptiness no form, no feelings, perceptions, impulses,
  consciousness. No eyes, no ears, no nose, no tongue, no body, no mind;
  no color, no sound, no smell, no taste, no touch, no object of mind;
  no realm of eyes and so forth until no realm of mind consciousness. No
  ignorance and also no extinction of it, and so forth until no old age
  and death and also no extinction of them. No suffering, no
  origination, no stopping, no path, no cognition, also no attainment
  with nothing to attain. "


http://www.kwanumzen.org/wp-content/uploads/Heart-Sutra-in-English-text1.pdf