You are very vague with the explanation of what you want to do here so I will do my best to try and help you.
You could put like a barrel or something on the ground and underneath it you could put "1234". Then you can have the player able to push the barrel and reveal the code.
HOW TO DO THIS:
. First add text to your layout (Double click white area and press add text)
. Next set the text to what you want it to say. (Click on the text and under properties in the side menus type in "1234")
. Create a sprite for the object that you want to hide the text behind and place it on top of the text.
. Now you need to do the code to move the barrel.
- If Player.x < Barrel.x
If Player is overlapping Barrel
Barrel.x = Barrel.x + 1
- If Player.x > Barrel.x
If Player is overlapping Barrel
Barrel.x = Barrel.x - 1
This will cause the barrel to move over by 1 pixel everytime the player is overlapping it.