Buyers and sellers cause prices to change as they decide how valuable each stock is. Basically, share prices change because of supply and demand . If more people want to buy a stock than sell it - the price moves up.
Stock represents ownership in a company.
Therefore, the price of a stock shows what investors feel the company is worth. Stock prices can change at any rate, some have dramatic swings in one day while others stay the same for a long time. There are hundreds of variables which drive stock prices, the most important of which is earnings . Think of earnings as the profit of a company, the money left after all expenses have been paid, this is what shareholders desire. There is also a common misconception that a stock that has risen will always come back down, this is false.