You hand over money today. The borrower pays you interest on set dates and gives the original amount back at the end. Everything else about bonds is detail on top of that.
A bond is a loan, just packaged so it can be bought and sold. You hand over money today; the issuer promises a fixed coupon on set dates and the face value back at maturity.
The price you pay today isn't always the face value — it moves with interest rates in between. Buy at $980, get $1,000 back, and that gap is part of your return too.
For the issuer: borrowing from thousands of investors at once through a bond is usually cheaper and more flexible than one large bank loan.
For the investor: a bond is the default place to put money that needs to still be there in 5 or 10 years. The coupon is contractual, and holding to maturity gets your money back regardless of what the price does along the way.
Governments run entire markets in their own bonds to fund deficits and roll over old debt. Companies issue them instead of borrowing everything from a bank.
Pension funds and insurers buy huge quantities, because a bond's fixed, dated payments are about the closest thing in finance to a liability that behaves itself.