These 20 comic panels need to be put in order to tell one complete story. A good place to start is with Justin (the boy on the right side of the panel). Follow how much popcorn he has left. There may be slides in between where he isn’t shown, but he’s a good place to start.
The panels with “READY”, “AIM”, and “FIRE” do not have any panels in between them.
When you are finished, you should be able to arrange the panels into a grid, with 5 panels horizontally and 4 panels vertically. When you do, the left-most pane in each row will have a solid white bar on its left.
Each row, when you read the letters from left to right (and top to bottom, for panels that show more than one letter) will spell a word.
When finished, the letters along the side spell STRANGER THINGS HAVE HAPPENED.