A ship board credit is money placed on your on board account that can be used any way you choose. You start the cruise with a credit.
While the cruise price is all inclusive (meaning accommodations, food and entertainment) there are things that carry an additional cost.
Alcohol, anything purchsed in the on board shops, bingo, coffee drinks (other than regular coffee) from the Cove Cafe, Palo,....all of these things are additional and a ship board dredit can be used to pay for them
Cash is not generally used aboard most cruise ships (unless there is a casino). Everything is charged on your Key to the World card and shows up in your onboard account.
A ship board credit would be used to pay off a portion of your onboard account.
Hope this helps.
