Click on the orange bird plate on the coffin, and if you picked up the drawing on the niche on the opposite wall, you'll start the puzzle.
This is what's known as a tangram. Pick up the golden pieces and arrange them in the outline at right so that they fill the entire outline without any pieces left over or overlapping.
Left click on a piece to pick it up and left click again to drop it where you want it to go. Right click after you pick up a piece to rotate it.
With the piece shaped like a slanted rectangle, if you right-click four time, it will flip as well as rotating. Handy!
There are lots of different ways to arrange the pieces, and any way you arrange them that they all fit is good; however, here's how I did it:
When you get the pieces arranged right, the coffin will open to reveal --
-- a skeleton, ew, and two strips of numbers that you'll need for a future puzzle --
-- opening Charlotte's bedroom door.