The first tune I ever learned? Impossible to say (mayhap I even learned tunes from the womb as my mother sang them!). The first tune I ever played on an instrument? Likewise, impossible to say; I took piano lessons as a child but I don't recall the tunes I was taught, and of course I played (or played at playing) the usual childhood instruments such as harmonica.

But I do remember the first song I learned to play on guitar, when I first picked up a guitar at age 19 and asked a friend to teach me some chords and songs: "Eddystone Light".