Minor seventh chords are a vital part of jazz-understanding them completely is vital to playing jazz (and will also be useful in blues and rock music). We will work first with Am7. The notes that make up Am7 are A, C, E, and G. You may know it in this form:
Play this chord several times and listen to it's sonority; compare it with this moveable voicing:
Notice that both chords are made up of the same notes, although the notes fall in a different order.