A stock share is partial ownership of a company.  For example, if ten thousand shares have been issued by the company, each share is worth one ten-thousandth of the whole company.  If the company grows and becomes more valuable, the value of each stock share rises.

The common way to buy shares of stock is in the stock market.  In theory, the price of a share is a fraction of whatever the company would be worth if it were sold.  On top of this go people’s hopes or fears about what the company will be worth in the foreseeable future, and their different timetables of how long they intend to hold the stock.  The market price at any moment is a rough consensus of the various valuations.  The price can bounce up and down as transactions are made during the day.  Generally, if a company seems to be successful the price of its shares will rise, and if the company is struggling the price of its shares will fall.

If you own stock in a successful company, the price per share will rise, and the value of your investment will grow.  In addition, many companies regularly pay dividends to their shareholders, a portion of the money that the company has earned.  If you own shares and reinvest the dividends by buying more shares, the value of your investment has the opportunity to grow in this way as well.