A song is sung, a tune is not. Chords are a part of an accompianiment for either of the above. A melody outlines some of the chords in the accompaniment. Basic progressions . . . hmmm. Different genres of music have different kinds of chord progressions. Polka music has chords popping up in places where some of us think they do not belong. Traditional Irish music usually has much a simpler chord structure than Americans prefer, therefore Americans will often add chords which do not belong. If you want to learn "basic progressions" get a good old Mel Bay beginner guitar book & train your ear--this will be "basic" to popular American music ! Learn the concept of I IV V V7. Good luck