Butch and Twinkie Nelson, for example, are a newly-married couple. Of course not. They clearly need to borrow money. So they borrow from a bank. Most people take out mortgages from banks when they buy houses.
People often borrow, also, in order to pay for college.
And a person who is starting up a new business will need to borrow money, too. If a woman named Fiona wants to open an arcade in a mall, she may expect to make a lot of money as kids pile in to play games, but first she needs to borrow money. Fiona needs enough money to rent space in the building, to buy or rent some pinball machines and other amusements, to hire some people work for her, and to place advertisements in newspapers. When it lends money, it charges interest. Interest rates change all the time, though, as the economy changes.