A sell limit order allows the trader to specify a price and the amount they would like to sell. The order does get filled only at or above the limit price.
E.g. With the trading pair of BTC/USDT, 1 BTC now equals to 6822.03 USDT. The sell limit is at 6900. Therefore, the price must go up till 6900(or above) to fill the sell order.
Once you click on exchange sell, it will then be reflected in your active orders, until it gets executed or cancelled.