Hmm you might want to search around the Stanford Encyclopedia of Philosophy for an answer that you like. From what I can tell, this piece on Hume might cover all the bases, but you should still search around anyways since that encyclopedia is awesome haha. http://plato.stanford.edu/entries/hume-moral/
The Standford Encyclopedia is incredible. I'd also suggest Philosophy Bro, if you want to take a more fun and entertaining route. I actually remember when Philosophy Bro first started as a comment on Reddit. Now whenever I find a new philosophy interest, I usually hit the SEP, then Philosophy Bro for a lighter summary, then onto the further research.
Haha I completely forgot about that site! The first day of my Legal Ethics class my professor started class by reading a piece from that site and we were all on the floor laughing. They class was somewhat of an into class so it had a bunch of people who were question whether or not they wanted to pursue philosophy, and Im pretty sure that one day got a few dozen people to change their major haha. But yeah, great site. Do you have the reddit comment saved? I would love to read it.
I love it! And your professor is awesome. I am the 'philosophy guy' (aka stoner guy) in my circle of friends and they often ask me to explain stuff for them. Sometimes I'm good at articulating and sometimes I'm not, but I always use Philosophy Bro as my backup or as my recommendation for further reading. It's a great way to introduce philosophy to people who don't have much experience in the area. I looked around and found the original post here. Enjoy :)