Yours does not look precisely like mine . So I can only explain how mine works and see if helps you . You never actually see the lancets as they are in a drum and the button to push the lancet into the skin is at the top and the white button moves the lancets in the drum
The way my accu check works is that there is a drum of 6 lancets . To prick your finger you press the top and a small prick is made . The lancet does not move on automatically so the white button is to move onto the next lancet in the drum you move it sideways and back i.e. will go 5, then it is ready for use then after next use you move it on to 4, etc.When you have used all 6 lancets you just pull the drum out from the bottom and insert a new drum and the pen will revert to 6 . The 5 to 1 at the bottom gives you the depth which the lancet will go 5 is the deepest and you can move round to get the right depth for the person who uses it .
Hope this helps