Just wondering if someone could give me some steps to working out the chord progression of sheet music ie. chord IV or II etc. How do I know what is what?
Simply put you analyze the score. You need some rudimentary knowledge of nonchord notes and the like. Let me give you an example to aid your comprehension. This is an excerpt from the piano piece La Romanesca by Franz Liszt. They key is a minor.
In the first bar, we have the melody in the right hand and the harmony in the left. The left-hand jumps from A to down to E and back to A hinting strongly at the tonic chord (a:i)
In the melody, the chord notes are the E, C and A with the D being an Accented Passing Note along with the B.
In bar 2 the harmony is still in the left hand and here we have an E jumping to a G sharp and back down to a B. This is the dominant chord of a minor (a:V).
The melody jumps only to and from chordal notes.
In bar 3 we know seem to have two chords in a bar in 3,1 we have the harmony jumping from A, E, and C. Tonic chord (a:i). In the melody, we have two chordal notes and a unaccented passing note (B)
In bar 3,2 we have the harmony jumping between E and G sharp. The melody only has chordal notes.
In bar 4,1 the harmony jumps between A, E and C and the melody only has chordal notes (C and A). In bar 4,2 the opening motif repeats.
In bar 5,1 the harmony jumps between A and E indicating the tonic chord and in 5,2 a third of the chord is introduced in the harmony.
The melody in bar 5 has the chordal notes E, C and A and has a accented passing note in D and B.
In bar 6 we have the harmony jumping between the notes E, G sharp and B. So here we are back to dominant (a:V). The melody only jumps between chordal notes.
In the last bar we have the harmony jumping between A, E, and C. Tonic again and in the second bar, we have the dominant chord again.
First of all, you need to find what scale the song is in (if any). This will be determined by the key signature and if it's a minor scale, there might be some accidentals.
After you've found out what scale you are in, you need to see what notes are being played and make out which chord they form. For instance, you might see that the notes being played are C,E,C and G. These notes form the C major chord.
Next, check the scale and see what roman numeral corresponds to that chord. For instance, In the C major scale, the C major chord would be I. On the F major scale, the C major chord would be a V etc.