Go to the graveyard. Go all the way the farthest (until you see the triangle symbol) and play Zelda's Lullaby when u are standing on top of it. A hole will appear in front of you. Go in it and keep going until you see a dead end (the entrance after passing the dead guys) and play your ocarina in front of it. It will teach u the Sun's song! Note: it lets you change day to night and night to day whenever you want!