Intraday trading is all about closing your trading positions the same day. You can buy in the morning and sell the shares before end of the day. Alternatively, you can also sell in the morning and buy back the shares before end of day. In fact, intraday trading is one platforms where you can actually sell shares without having delivery in your demat account.
Intraday trades are squared off the same day, so they do not, in any way impact your demat account. You can define the order as a Margin for Intraday Square-off (MIS) order and you can get intraday trading limits up to 5-10 times the transaction value, based on the volatility of the stock.