The first day
Blue Prince opens in a garage with one door. Behind it is a drafting table and a small grid. Your job each day is to add rooms one at a time, connecting doors, until you either reach Room 46 or run out of moves.
You do not need to win on day one. The point of early days is to learn which rooms do what, where items hide, and how the numbering on the draft menu works.
How a day flows
You start with a set number of steps and a draft pool of rooms. Pick a room from the menu, place it against an open door, and walk through. Each room you enter can give you an item, a puzzle, or a dead end.
When your steps or your draft options run out, the day ends and the house resets. Anything permanent you unlocked stays; the rooms do not.
Habits that get you deeper
Draft toward a goal instead of grabbing the prettiest room. If Room 46 needs a specific wing open, build the path first and fill the sides later.
Read the room description before you commit. The draft menu tells you a room number and type; that line is the difference between a room that helps and a room that wastes a door.
The full room list lives in the room database, and every item is in the item database.