The hammer-attack is performed by any left hand finger being firmly and accurately placed onto the fretboard using enough force to produce a sustained sound without picking the note. The hammer-attack is similar to the hammer-on except there is no preceding note involved.
Practice the hammer-attack in example 391 starting with your left index finger. Try to play the example using the other left hand fingers and move it onto different frets.
Each of these examples start with a hammer-attack followed by a hammer-on.
Each of these examples start with a hammer-attack followed by a cross-hammer.
Transpose these examples onto different strings and frets.