One of Little Nightmares' first puzzles is also its most challenging. The puzzle in question involves a switch, a box attached to a chain, and a long climb up.
You might be frustrated by this puzzle since it isn't obvious what you need to do, and if you fail you can fall down and die, forcing yourself to climb all the way back up. Thankfully, we have a solution for you.
To start, pull on the lever on the far right. This will move the box upward and make it available for you to move. From here, make sure the box is positioned away from the platform that you're standing on. You're going to utilize momentum to solve this puzzle.
Pull the lever to the right to make the box move toward your platform. As it approaches, quickly pull the lever to the left and then run and jump onto the box. If you time it right, the machine's transition period between moving the box right and then left will provide you with enough time to jump onto the box.
This took me a couple tries and seemed impossible at first. Keep trying and you should be successful. Good luck!