This is a programmable combination lock. Insert the pins on the program wheels to make the combination lock open by different combination digits. The dial goes from 0 to 39.
This combination lock uses the same dial to enter the code and open the latch, unlike other combination locks found on Thingiverse. You can built this into your own safe door, or use the   supplied case, meant for demonstrating how a combination lock works.
You should turn the dial 4 times counter clockwise to the first number, 3 times clockwise to the second number, two times counter clockwise to the third and then clockwise until the latch opens.
Watch this video to get details how a combination lock works and how to dial the numbers: https://www.youtube.com/watch?v=jz2WVSoQBxM