I use points but do not know what credits are - they appear to be the same thing but there must be a fundamental difference.
 
Can anyone enlighten me please?

I have no idea. All I can say is what I use each of them for. I use points for people to accumulate and use towards future purchases. I use credits as a "store credit" type where if someone isn't really happy with a purchase and would like a refund or something, I may decide to issue them a store credit.
 
That's how I utilize it, but to answer your question, I'm not exactly sure...

Credits is like cash. For example, you can refund or put discount $ as credits in user's account so they can use the available balance to apply to their future purchases (you can turn on the option to show credit balance at the check out). Negative credit balance (owe) should work the same way but I have not tried it yet.

Thank you guys - we are steadily writing an alternative manual?