trading takes place when u place the order to the exchange from your DEMAT account from your brokers web portal or via his app . if the settlement is not done with the trading +2 days then the exchange automatically takes the order to auction and dose it next day with what ever is opening price and the money is taken from the brokers deposit with the exchange. SEBI ensure the process is smooth. stock trading can be done only if you can calculate the risk Vs reward Ratio and it has to be done only with knowledge and discipline. if the quoted price is higher then the order will be executed immediately with what ever the price seller is ready to sell at. their are 3 types of orders market order ,limit order and stoploss order.demand and supply decides the price of stocks.the price of the stocks does not effects the business of the company.