The stock exchange is where companies willing to publicly sell off ownership of their companies do such trades (they have to be approved of course, and follow a lot of regulations). In America the 2 largest ones are the New York Stock Exchange located on Wall Street, and the NASDAQ which is digital.

These pieces of ownership, shares, sometimes allow you to have voting rights as well as receive profits, dividends, which are in-line with the % of the company that you own. Now, not all shares come with either/both, so just do some research (you can just Google: “Does Apple stock pay dividends?”). You could cash out these dividends, but since it usually is a few pennies/bucks for most people, they instead choose to opt-in/enable a feature called Dividend Reinvestment Plan (DRIP), where they money is instead used to buy more shares of that company, that way you earn more shares and also earn more dividends, and this repeats and repeats (you could do this all manually especially since nowadays it is commission free and fractional shares can be bought; it used to be much more appealing before this, as now you could take the money and buy fractional shares in another company if you wish).

A broker is a person/app that handles the transactions (think Leonardo DiCaprio in Wolf of Wall Street); you yourself can’t just walk up to the NY Stock Exchange on Wall Street and do business). Historically brokers have charged commission fees but now most are free (they make money from offering other services, such as financial advising, they also require the money you wish to use to make purchases to be in their fund for them to invest in, rather than just charging your bank account).