You enter the directions listed by clicking the corresponding side of the safe dial. Once done, you pull the lever to open it. When the game gets more complicated via the writer of the note encoding false data, there's a clue on the note about which color is correct.
I had trouble figuring out that game at all.
Part of it was that I didn't realize you actually had to click and drag the handle, so even when I'd done it right, when I clicked on the handle it didn't unlock.
The other thing that confused me was how little the wheel spun. It's so different than a real lock that I assumed I was doing something wrong.
Those two points of confusion combined to make me experimenting with the wrong things to make the puzzle work. I was sure I was screwing up the wheel somehow.