Simply put, cash is cash. That's the amount of money in U.S. Dollars you have in your account. 

Your credits are the balance you use to play b spot games.

You make deposits into your cash account and use the money to buy credits. You play credits in b spot games and any real money prizes you reveal will be added to your cash account.

You can't withdraw credits. They have no monetary value. They can only be used to play b spot games and reveal any cash prizes you have won.