When you first "get it" you will be elated! At first the harmony is elusive..but..any instrument...when a chord is played...has several of the harmonics within it. Just find the one that matches "your" vocal range. I started this way and can find three or four harmonics this way whithin a chord. Listen to the master Dr. Ralph Stanley, he will sing more than one harmonic at the same time for any given melody note. For a beginning I think singing "rounds" will allow searching for that elusive note over and over till you find it. Try the chosen round in all the keys until you hear "your" key. Cheers!!