When the buyers and sellers price meet the trading is executed.
Both the buyers and sellers exchange the shares through brokers.
The brokers has to be registered in SEBI.
Buying stock from BSE and sell it on NSE is possible only when the brokers has to deal with both the exchange and companies should be listed in both the exchange.
In Intraday trading buying and selling or selling and buying the stock on the same day. It is not possible to transferred the stock from BSE to NSE.
Stock trading is the business and not gambling.
Stock price are decided by the buyers and sellers based on demand and supply. Stock price does not affects the monetary aspects of the company.