The swivel body has two halves, two screws, and one ring.
Place the two halves together to form the swivel body.
Screw in one of the screws into the middle hole. This screw should stay tightened always as it holds the swivel body together.
Place the ring on the bottom left of the previous picture into the remaining hole. Notice that the ring has two teeth and must be rotated properly to seat into the hole.
Once the ring is inserted, screw in the final screw partially. This is the "set" screw used to set the fixture arm.
Now you can rotate the swivel portion on the left up or down until it is in position. Once it is in a good position, screw in the set screw to hold in position.