Trading is buying and selling the shares. Price of the shares determined by buyer and seller.Long position is buying shares when the price is going up and long unwinding is sell the same. Short position is selling the shares which we didn’t buy yet.Broker is responsible for executing the order.IF there any issue in counter parties, exchange settle the same by getting money from broker. Trading done in same day is called as Intraday trading. Buying shares hold it for sometimes and sell later is defined as Position trading.