Stocks and shares are a piece of a company. Each company may have a different amount of shares available, and the amount of shares the company releases for sale to private investors will reduce the ownership of the company by a percentage. For example, a company may have 10,000 shares. Someone who invests in 100 shares would have a 1% stake in the company. It would be rare, however, for a private investor to own as much as 1% of a company.
Shares don't have a fixed price, a share's value can go up and down and is affected by various things. For example, interest in the company, such as a takeover bid or a merger that can make the company a more desirable investment, or by some negative publicity that may make shareholders sell, and the prices drop.
