Insert a wooden dowel into the chuck. Thanks the part facing camera in the last 2 pics. Flip the black handle over, so it rests against the stop. It's in the fully open position now, move it to fully closed. Rotate handle. The cutting head (like in a hand crank pencil sharpener) will cut down the diameter of the dowel.
You can see the adjustable stop in the 2nd pic, so you can set the length of the turned down portion Keith