After getting it, go back to Pokémon Tower and prepare for a long journey. Channelers are hanging around possessed by ghost Pokémon. Fighting Pokémon are useless here, because ghosts are immune to physical attacks.
There are a lot of ghosts around, but they can be identified with the Silph Scope. Catch a Gastly (unique to this place) and a Cubone here. Soon, you will fight Cubone's mother, a Lv.30 Marowak. You can't capture her, but if you win, her soul will be freed. Beat the Rockets to rescue Mr. Fuji, who'll give you the Poke Flute. Now, go back to Celadon.
Celadon City Go West from Celadon City. On this road, a Snorlax is sleeping, and you
must wake him up. If you have the Poke Flute, you can wake him up and fight him. Cut down a nearby bush and go up and left. Go through the building and into the house you find. The girl inside will give you HM 02 (fly). Used in battle, it is similar to DIG. Used outside, it will bring you to a Poke center already visited.
