what is the keypad in the beginning area for? is it only for subs or something or do you get the code later on?
Thats the entrance to the debug room. The 5 digit code is easy enough to guess. The hints are is numbers that spell and word and that word is the main focus of the game.
If you cant figure it out you can talk to the NPC that appears in the adventure zone area after you view the credits and he will straight up tell you the code.