Credit Card: credit cards are lines of credit. When you use a credit card, the issuer puts money toward the transaction. This is a loan you are expected to pay back in full (usually within 30 days), unless you want to be charged interest.
Debit Card: any time you use a debit card to buy something, money is deducted from your account. With a debit card, you can really only spend the money you have available to you.
CVV is Card Verification Value (credit card security)