Select all of the parts of the arm then make it a movie clip named Arm.
Double click on the arm to edit it.
Select the bone tool,
then click the top of the arm, the shoulder first. The first place you click will be the anchor.
Next click the top of the lower arm, then the hand. After you have selected the three joints of the arm, click the selection tool.
Grab the hand and move it around. The arm bends at the joints but it stays connected.