How do currency/rewards work?

[longbich]

If you open up either of these nav buttons you get a list of what you can buy and the number of credits needed.
Where is it explained about these options? What are the credits awarded for? How do you earn them?
I looked thru the FAQ's and when I put one of those words in (Rewards/Currency) there is no response.

[carl6969]

The Rating\Credit System Explained