Fretboard diagrams are used throughout this book to show you where to place your left hand fingers. A fretboard diagram is a grid of horizontal and vertical lines representing the strings and frets of the guitar.
An open circle shown above the nut indicates an open string, i.e., the string is played "open" without the need of holding down the string at a particular fret. The following diagram shows the first string open, the note E.
A black circle drawn on a string indicates a fretted note. The number inside the circle refers to which left hand finger is used to play that note. The following diagram highlights the note on the first fret of the first string (an F note), to be played with the first finger.