Shares are small pieces of a company. Shares can be bought by humans, companies, and mutual funds. When buying shares in a company, the buyer owns a small part of that company. The price of a share can be based on many different things. The main thing that affects the price is the balance between supply and demand. If many buyers want to buy a stock the price goes up. If there are more sellers than buyers, the price goes down.
Some buyers trade shares in stocks through a stockbroker. A stockbroker is a person who buys or sell stocks for their customers. A stockbroker can also help customers make choices in stocks. Their advice is based on public information about the companies.