Please keep me honest. I know I'm getting ahead of myself lesson wise but...
Most blues, rock and country use a standard chord progression of I IV V. If I have a song in the key of C the chords would break down to:
I - C, ii - Dm, iii - Em, IV - F, V - G, vi - Am, vii - B
so if I have a song, say Kum Ba Yah in the key of D it happens to use I - D, IV - G and V - A7 (V chords are often made to 7 or sus 4 from my understanding to add variety and emotion).
I can change the chord markings on the lead sheet to I , IV and V. Then I could, if my understanding is correct, use the I IV V from any key and play the same song (chords only obviously) so I could accompany someone that sings or plays in a different key.
I kept this kinda simple so I dont confuse myself, but I think Im on the right track...
All input welcome!