Fretting is pressing the strings down against the frets to shorten or lengthen the string and create higher or lower tones.
The fretting hand also does more than just press strings down. It can can pluck the string [pull]. It can mute, which is vital in creating chords with clarity and building your rhythmic skills. It can create tones without the string being picked by the motor hand [hammers].
The fretting hand is integral to creating beautiful tone and rhythm.
By studying our touch [level of pressure and how we approach/press fretted tones] and after-touch [release], we develop layers of tonal control.
For fretting, we also consider our hand shape. Two general hand shapes give us each pole of the possibilities: classical and rock.
A classical shape is the 2 and 3 fingers straight on the fretboard, with 1 and 4 fingers curved on each side. In the picture above, I’m leaning out to show the edge of this shape range. We can use the outside pad edge of the pinky.
The rock shape is angled with the 1, 2, and 3 doing most of the work.
And, anywhere in between. Fretting hand shape is determined by context.
The fretting hand can also bar [barre]. This is playing the same fret on multiple strings with the same finger. We can bar 6, 5, 4, 3, or 2 strings. Depending on the which strings are being barred, they can be adjacent or non-adjacent strings.