A hammer-on is a left-hand technique that enables you to play two consecutive ascending notes by picking only the first note. The hammer-on derives its name from the action of your left-hand finger, which acts like a hammer striking the fretboard, causing the note of that fret to sound out. This technique makes the connection between the notes sound smooth — far smoother than if you simply pick each note separately.
An open-string hammer-on (or just hammer, for short) is the easiest kind to play and is shown in the following figure.
In tab (and standard) notation, the letter H with a slur (a curved line) indicates a hammer-on. (The slur connects the first fret number, or note, of the hammer-on with the last, and the H appears centered over the slur. If two Hs appear over the slur, the hammer-on involves three notes.)
Pick the open G string (the 3rd string) as you normally do. While the open string is still ringing, use a finger of your left hand (say, the first finger) to quickly and firmly strike (or slam or smack, as you prefer) the second fret of the same string.
If you bring your finger down with enough force, you hear the new note (the second fret A) ringing. Normally, your left hand doesn’t strike a fret; it merely presses down on it. But to produce an audible sound without picking, you must hit the string pretty hard, as though your finger’s a little hammer coming down on the fretboard.
The following figure shows a hammer-on from a fretted note on the 3rd string. Use your first finger to fret the first note at the fourth fret and strike the string; then, while that note’s still ringing, use your second finger to hammer down on the fifth fret.
