Do not skip the opening scene. Afterwards you will unlock:

Open the "residents" tab at the top and click through the bios of all 8 characters for 8 more achievements.

Back to the "play" tab.

Each green paragraph is a different location you can click to go to.
After finishing the first location, a "You brought everything!" option will appear, but ignore that for now and finish all 5 regular locations first.

At each location you need to:

1. Die
   By letting the red bar in the top left corner fill completely. Repeatedly click on a monster to fill the bar quickly.
   
2. Find 5 Items
   The "Task and map" tab lists 5 items you need to find. I've listed which room everything is in below. Travel between rooms by click and holding on the door, do the same on an item to pick it up.
   
3. Exit
   After finding the 5 items, the game won't automatically finish the level. Go to Room 10 then exit to another room to bring up the "Task is complete!" screen and for the game to recognise that you've finished the level.

Locations are given randomly. If you don't get the one you need, enter any level and exit to get different ones.

room 3: picture
room 4: pullover
room 6: dog collar
room 8: photo album
room 10: plush toy

room 2: photo
room 4: skull
room 6: willow branch
room 7: children shoes
room 9: handful of earth

room 2: paper
room 4: bulky bondage
room 6: stethoscope
room 7: nameboard 101
room 8: scalpel

room 2: class register
room 4: cravat
room 7: microscope
room 9: cup
room 10: love letter

room 2: mug
room 5: ball
room 6: page from the book
room 8: xylophone
room 9: kids sandals

After finding all 25 items, click the "You brought everything!" option to be brought to the storeroom. Reveal all 25 shadow items on this screen (click and hold) to start the ending. Probably best not to skip the ending either.