Every now and then -- usually just after you hear "eerie singing" down at the bottom of the stairs -- you'll come up to the second floor to find a note on the table next to the sleeping bags addressed to Nancy.
Each note tells you to do something. If you do it right, you'll know right away because the note disappears from your inventory and something happens that moves the game along.
Unfortunately, the notes all consist of tricky riddles phrased in bad poetry, so they're pretty annoying. But Nancy will help you figure them out; read her journal for help here.