Where do you use the passwords?
Tab to write messages.
That's not what I meant. I found a billboard with a sequence of numbers and letters, so I was wondering if they have a use, and where to use it.
Yep, that's what I mean. Have you noticed that picking up a bottle sometimes changes day to night or vice versa?
EDIT: Either of these things, or are you talking about something else?
If the billboard says 'write,' you tab to type a message.
If you get a billboard that says 'Password:[something],' then you have to take 100 parcels/discs to the red door to open it. It takes you to a platform with a computer and the password is used to extinguish all other life in your universe (every player has their own - the rain/bottles are interdimensional)