What is a loan and how does borrowing work?

Imagine you're standing in front of the coolest bicycle in the shop window. It costs $200. You have $5. This is a problem. But then your friend says something interesting: "I'll lend you the money now, and you can pay me back later." Suddenly, the impossible becomes possible — you could ride that bike home today.
That's a loan in its simplest form: someone gives you money (or anything valuable) right now, and you promise to give it back later. Your friend becomes the lender — the person loaning the money. You become the borrower — the person receiving it. The bike shop gets paid today, even though YOU don't have the money today. Everyone wins, as long as you keep your promise.
