Parables are tales meant to teach a lesson or to hide a truth in words that will not be understood by the uninitiated.  The Bible is full of parables.  Jesus spoke in parable frequently.  Many other spiritual writings from other religions are full of parables also.  Joseph Campbell tried to teach us that there were important truths and lessons hid in the common myths found all over the world.  But parables are not just in written stories.  They happen live, around us, all the time.  The way a tree grows can be full of symbolic meaning.  The song of a bird or the path of it's flight.  Just because something is real, doesn't mean it can't have a symbolic meaning also.  And, of course, there are the symbols and parables that come to us in dreams.  So it is helpful for our spiritual growth to learn to understand the symbols of parables.