Imagine a company's ownership divided into 100 equal slices. If you own one slice, you own 1% of everything that company has — its cash, its buildings, its brand, and its future profits. That's exactly what a share of stock is: a slice of ownership in a real business, not a loan and not a coupon.
Companies usually start out privately owned by founders and early investors. When a company "goes public" (an IPO), it sells slices of itself to anyone willing to buy, in exchange for cash it can use to grow — hire people, build factories, develop new products. In return, the company gives up some ownership and some control.
As a shareholder, you get real, if not guaranteed, upside: if the company grows and becomes more valuable, your slice is worth more too. Some companies also share profits directly with shareholders through dividends. But none of it is a promise — unlike a bond, which contractually owes you your money back plus interest, a stock owes you nothing. If the business does poorly, your slice can be worth less, or even worthless.
Correct moves you up, wrong moves you down — reach 100 to master this lesson.