You can use it when there is small tree in your way and after you beat misty she gives it to you
You can use the move cut once you have defeated the second gym leader
use cut on the door.
use cut
you've got to use cut.
use cut. read up on your braille.
use strength or cut that's my opinion
You need to use Cut on the metal door
The cerulean city gym.
Answer:Have a Pokemon use the HM move Cut on the door.
You walk up to the door and use cut.
Go up to the wall and use HM cut
it says cut the door, so go to the door then use cut with a Pokemon that knows cut and the door will open.