The lower circuit is the lowest price that a stock can fall in intraday.

Lower Circuit=Only Sellers, No buyers

So, you cannot sell the shares when the price hits the lower circuit. If you have holdings of that particular share then you will have to wait for the next day or you can also place an AMO order.

If you have bought the shares for intraday and if the stock hits the lower circuit, then your stockbroker will buy the shares in the auction and squares off the positions.

The brokerage charges and the auction price will be deducted from your Demat account.