juststartn,
DOn't worry about not being 'up to speed'. It's not a race.
There are lots of references - both online and off - to help you understand what the Church teaches on the matter of jusftification. A good place to start is at
New Advent: Justification. THis will give you a good overview and a starting place to address things with your friend.
Keep in mind a few things during your discussion. Make sure you guys are talking about the 'right' words (ie, that everyone knows up front what words like 'redemption', 'justification', etc., mean. It will save much time if you don't have to go back midway through the discussion and clear up definitions). Second, as you've already done, if you aren't sure of something or the best way to present it or the best way to respond to something, don't be afraid to say, 'Hmm, I'm not sure. Let me do some research.' or something along those line.
After looking over the article at NewAdvent, see what kind of more specific questions you can come up with.