I just ordered a Credit card and it has my former last name on it instead of my new last name. Can I still use it or do I have to get a new one?
It'll be fine 99% of the time, but it could occasionally cause issues. Some places ID for credit cards to prevent fraud, even though it's technically against their agreement with MasterCard etc. to do so. So you might occasionally be refused if the name on your card doesn't match your ID. There might also be occasions where your credit card could be used as a form of ID (e.g. when you forward your mail to a new address) but you can't use it because the name is wrong on it.
So long as you have a backup card, it's not going to cause you major problems, but I'd get a new one with the correct name anyway.