After reaching the barn in Life Is Strange, you will come accross a padlock hidden on the floor at one point, and you will need to find a way to open this. This part is a bit of a puzzle, and here's the solution to opening the padlock in the barn.
First, attach the hook to the padlock. Now head to Chloe, and next to here is a platform that you can climb up on. Go up there, and then pull the engine down to climb to the next level. At the top, go to the other side of the platform to get a photo of the owl (optional), then rewind time to get the engine back up. This allows you to attach the rope to the enigine, where the other part it still attached to the padlock at the main floor.
Once this is done, push the engine down, and the padlock will crack open and reveal a secret door down below the main floor.