You must pay your debts, but sometimes you cannot.
If you owe money, the money you owe is called 'debt'.
The person or company you owe is a creditor.
Sometimes a creditor hires another company or a lawyer to collect the debt from you. A creditor can also sell your debt to another company. The new company or person is called a debt collector. The debt collector is also a creditor.
Your creditors can take you to court to get the money you owe. They may be able to take your property or your income to pay the debt. When you cannot pay your debt, you may have a right to keep some kinds of income and some property.