The notes
The tune ranges from E4 up to F5, the upper middle of the keyboard. It uses u (E4), o (G4), O (G♯4), I (F♯4), p (A4), a (B4), s (C5), d (D5), f (E5) and g (F5), and it opens on a lone A, p, as a pickup into the first bar.
The swing in the spacing
Greensleeves moves in a swaying triple time, and nearly every bar has the same long-short pattern. The sheet shows it with a dash after the long note and the short note glued to the one that follows: f - gf (long E, short F, E), o - pa (long G, short A, B), p - Op (long A, short G♯, A). A note followed by two dashes, like s - -, lasts a full two beats.
The first line descends at its end to u, the low E, which leaves the melody hanging. The second line is the answer: it rises the same way, then turns home through ap O - IO to rest on A, held for three beats.
From notes to music
Find the keys first, with no thought for rhythm. Once the order of notes is in your fingers, listen to the tune at normal speed and copy the lilt: lean on each long note, let the short one fall lightly into the next. On a computer keyboard the two black keys come only near line ends, as O (Shift+o) and I (Shift+i).
Where the tune comes from
Greensleeves is an English ballad tune. George Grove’s Dictionary of Music and Musicians records that a ballad called “A new Northerne dittye of the Ladye Greene Sleeves” was entered in the Stationers’ Register in September 1580, and that Shakespeare mentions the tune twice in The Merry Wives of Windsor. Grove thought the tune itself older still, and lists other names it went by, “The Blacksmith” and “The Brewer”. The version here is the melody as it is commonly played today.
Another tune from the same public domain shelf is Beethoven’s Für Elise, also in A minor.