You will notice that you can move the arm into positions that a real person could not. We will not add some constraints to the movement so that the arm can only move to natural arm positions.
Change the zoom level to 200% so that you can see the joints clearly.
From inside the arm movie clip, drag the hand down so that the arm is against the imaginary man's side.
Click the upper part of the arm to select it.
Int the properties window select constraint in the joint rotation:
Set the constraint for the shoulder as shown in the illustration:
Set the constraint for the elbow and hand in the same way.
When you run the movie, the user will be able to drag the arm and reposition the arm.