All the answers here! The main goal in 100 Doors is to escape the room. Using all the possibilities of the device you need to open each of 100 doors and move the doors to the next Level.
Search for hidden objects, solve puzzles and use an items to do this!
Rip the wallpaper on the top left to reveal 231
Open drawer 2 then 3 and 1 to reveal the key.
Grab the handle on the floor and then put it on the door