It includes any unpaid balance from last month, new purchases or cash advances, and any finance charges or other fees. The smallest amount you can pay and still meet the terms of your card agreement. If you assume that the minimum is all you need to pay, you could owe finance charges you didn't expect. When it comes to joint accounts, how each individual handles the account reflects on the other person. While you may handle your account responsibly, someone on your account who has not been equally responsible can affect your credit rating.
Interest is the cost for the convenience of paying for purchases over time.
It's what you would pay over the course of a year. When you make a payment, typically your dollars go to pay finance charges first, then your balance. So if you're making just the minimum payment, you're paying mostly interest. You'll reduce your balance quicker even if you pay just a little more. Some cards, like your Citibank card, give you an interest-free grace period.