Just click on SELL button -> Select Market (if you want to sell at current market price) -> Type in the Quantity (in this case 50) and hit the SELL button. If you want to Sell at a particular price instead of the current market price then select Limit and type in the limit price (your target price) with the quantity mentioned as 50. This will open a Limit Sell order and will get executed once the price reach your target.

Rajib Bhattacharjee
Intraday Trader