Buyers and sellers meet at a common market place (stock exchange) They bid for various stocks by entering into different counters. After finalising on the price, the buyer of the stock gets a share certificate in a demat form and the seller gets money.
Yes. It is possible. They can buy from one exchange, wait for delivery of the shares into their demat account and then they can sell it on another exchange. The only limitation is that they cannot do this intra day.
The exchange is programmed to take the best available price. If you quote Rs.20,000 for a share that is being traded at 2000, the exchange will override your quote and place a buy at the price of 2000
Long is when you buy the shares first to hold for a period of time
Short is when you first sell the shares and buy them before settlement time that day
Long unwinding is when you sell a stock after holding it
Short covering is when you buy a stock after selling it earlier that day