How is the price of securities formed?
The price of a share depends on supply and demand. For instance, there is a positive news about the company which projects big profit for the next five years. Seeing this, investors start buying company's shares for their portfolios. At the same time, owners of the shares don't want to sell shares with such potential at a previous price and raise it. If buyers agree with the price and buy shares at it, the share price rises. The higher the demand, the higher the price - the rule of any market, and stock exchanges are no exception.