A share makes you a part-owner of a business. A bond makes you a lender. You hand over money, the borrower pays you interest, and on an agreed date — the maturity — they repay the original amount, called the principal or face value.
The interest payment is called the coupon. The yield is that income measured against what you actually paid, which is why two people holding the same bond can have different yields: one may have bought it cheaper than the other.
Governments issue bonds to fund spending without raising taxes today. Companies issue them to build factories, buy rivals or refinance older debt. US government bonds are called Treasuries, and are named by how long they run: bills (under a year), notes (two to ten years) and bonds (twenty years and beyond).
Companies issue corporate bonds, which pay more than government bonds because a company is more likely to fail than the US government. States and cities issue municipal bonds, where the interest is often exempt from federal income tax.
Most people never buy a single bond. They buy a bond ETF: one fund holding thousands of bonds, which trades on the exchange like a share. That makes bonds easy to buy — and it also means the fund's price moves every day, even though each bond inside it has a fixed repayment date.