Minor chords [I'm trying to remember this without a guitar!]. If your root chord is Em, you would also use C and D, as if you were in G major. So... that would be root, minor 7th and minor 6th. I think. Go on, all you experts out there, put me right. As I understand it, a riff is a melody played by the lead instrument as a one off as part of being a show off. A lick is a sequence that is repeated over and over again. Hope that helps.