That "outside black piece" is called the eccentric crank.
It can go one one of two ways. Make sure you mount it so that the arm is close to the center/axle of the drive wheel, not pointing away from the axle.
When you put the long screw into the eccentric crank, paint the threads with clear fingernail polish. That will keep the screw from getting loose, but you will still be able to remove the screw when you want to do so.
