In the Scene palette, expand the figure you want to parent to until you see the part you want to attach the figure to - I would agree that in this case that would be the chest. Then drag the second figure's entry in the Sceen palette onto that part and let go. That should be it - if it jumps, rather than staying put, Undo and then go to the Scene palette option menu (triangle button at top-right) and click Parent in place, so that it has a tick next to it, and then try again. Hide the parts of the second figure that you don't need  -presumably the legs, head and trunk here, by selecting them all and then clicking the Visible button in the Parameter palette. Be careful not to apply poses that move the body or hip to the parented figure as those will displace it with respect to the first (you can of course deliberately adjust the position of the figure to achieve the effect you want).