Learn the half steps of the musical alphabet. This will be essential to forming chords. The half steps are A, A#/Bb, B, C, C#/Db, D, D#/Eb, E, F, F#/Gb, G, G#/Ab.
Learn where notes (A, B, C, D, E, F and G) are located on the treble and bass clefs. The notes progress up the musical staff, alternating between resting on a line or in a space. You can study a diagram of the staff lines for the bass and treble clefs to become familiar with note placement (see Resources).
Write the root of a chord. The root is the note after which the chord is named. For example, the root of a G chord would be G.
Write notes that harmonize with the root above or below the root note. You can find the harmony notes by counting intervals. A major chord is composed of the root, plus four half steps (called a "third") above the root and seven half steps (called a "fifth") above the root. For instance, a G major chord would consist of G, B and D. A minor chord is composed of the root, plus three half steps (called a "minor third") and seven half steps above the root. Therefore, G minor would be written as G, Bb and D. Whenever you have a flat (b) or a sharp (#), write the symbol next to the note.
Write inversions of the chords based on which note is on bottom (in the "bass"). A chord with the root note in the lowest position is a tonic chord. A chord with the third in the lowest position is a first inversion and a chord that has the fifth in the bass is a second inversion. Choose your inversions based on what best fits the sound of the song.