Wind's Requiem

The "Wind's Requiem" is the first song Link learns in The Wind Waker.

Learning Location
The requiem is learned upon reading Zephos's monument behind Dragon Roost Island with the notes inscribed on it. This melody allows Link to control the direction of the wind, but it only works outside in the overworld.

Uses
The "Wind's Requiem" plays a major role in The Wind Waker, for it is necessary to constantly change the direction of the wind in order to navigate the many islands of the Great Sea, as well as to favor flight with the Deku Leaf. In later parts of the game, playing this melody on certain tiles will make a treasure chest appear, usually containing a Triforce Chart in the Great Sea or a Treasure Chart in some dungeons, having a similar role to Zelda's Lullaby in Ocarina of Time.

Trivia

 * Interestingly enough, the "Wind's Requiem" can be used to change the direction of the wind during the final boss battle against Ganondorf on top of his tower, although doing so does not change anything with the outcome of the battle.
 * "Epona's Song" has the same directional notes as the "Wind's Requiem".
 * Similarly to Zelda's Lullaby, the Wind's Requiem is another alleged reference to the Triforce, with one directional note for each crest of the Triforce.
 * Contrary to popular belief, the Wind's Requiem can be obtained as soon as the Wind Waker is aquired. If the song is played at the start of Dragon Roost cavern (the room you get the first bottle in), the wind will blow in one direction continuously until the room is left or you fall in the lava.