The stock trading includes the stock exchange, broker, depositories and traders. All the activities are regulated by SEBI.
The stock exchange is the place where the brokers can purchase the shares by the orders placed by the traders and the money is kept in Depositories. The purchase of stock happens in primary and secondary market.
The share holder are owners of the company.
The company decides to go public when fund are required for business expansion through ipo. The shares purchased in IPO cannot be refunded and can be sold only in secondary market. The allotment of dividends or bonus can only be decided by company and the share holder has no rights.