Closing a work order does nothing to on-hand quantities.  To pull components from stock that are used by a work order, you need to either use WO-G to issue them or backflush when entering finished production at WO-I.  WO-I is also the program used to put the finished item into stock so that it can be sold or used as a component in a higher level assembly.
 
You can use WO-I to backflush components, put the finished item into stock and close the work order all in one step.  Finally, you need to post an invoice to a customer to pull the finished item from stock and register the sale.