Stock is a game tool. You can buy and sell stock as an investment in the stock tab. Message investors and get messages.
Your company progress is tracked by your stock value. As your company value increases so does your stock price. Expand your airline in all direction to raise your stock value. Add airplanes, routes, employees, save fuel money. Be sure to buy your friends stock when it is available and encourage them to keep their stock prices up so that your investment in their airline grows.