This one isn't brain surgery - the longer you have debt, the more interest you pay. It pays to get out of debt as fast as you can.
Debt is what you owe - it comes in many forms, including mortgages, personal loans, credit card balances, hire purchase agreements, loans from family.
Money paid in return for the use of money. If the bank is using your money (in a savings account) they pay you interest. If you are using the bank's money (via a loan), you pay the bank money.