If you're still in edit mode, leave edit mode (tab key).  Select the armature and hit Ctrl-tab.  You are now in Pose Mode.  The armature should now be blue.  You can leave pose mode by hitting Ctrl-tab again.

Select the top bone and rotate it (r key).  The top sphere should go with it, the others should stay still.  You should get something like the image above.  Try rotating the bottom bone too, all spheres should move.  When you leave edit mode everything should stay posed.