Left Hand Position

Position, as it applies to the left hand, is determined by the fret in which the first finger plays or would play.
Each higher fret is assigned to the next higher finger.
In written music, Left Hand Positions are represented by Roman Numerals.

In Fifth Position (V), for example, the first, second, third, and fourth fingers cover the fifth, sixth, seventh, and
eighth frets, respectively. This is similar to a zone defense.

Fifth Position (7th fret is marked):

In First Position ( I ), the first, second, third, and fourth fingers cover the first, second, third, and fourth frets, respectively. First position is the most common position for the left hand because approximately 2/3 of all of the notes on the guitar are available in First Position and 3/4 of the most commonly played notes can be played in First
Position.

First Position:

Remaining in one Left Hand Position at a time is beneficial because it shortens the playing field to only four frets and gives you access to 30 notes in any given Position (four notes per string and the six open strings).

It is important to note that, although the fret in which the first finger plays determines the Position. ANY finger can
establish a new Left Hand Position.

For example, if you put your third finger in the sixth fret, you have established Fourth Position (IV),
even though the first finger is not yet playing.