Stop loss, is the price where your sell will be triggered, meaning you are ready to sell at all cost at this price and below( BUT!! this low price has a floor, which is set by your lowest selling price) Any price below this lowest selling price would not be executed.
E.g. you wanna sell Singtel, stop loss at 3.95, lowest at 3.93.
In this case, your stop loss will be triggered once singtel price falls to or below 3.95. It will attempt to sell between the price of 3.95-3.93. Let's say singtel falls from 3.96 to 3.92, your order will not be executed.
Why have this? To prevent huge losses.
The standard sell can execute your 3.95 and below already. Meaning, if you die die wanna sell, set a low enough price and it will confirm be sold.
The 'stop loss, lowest' set a floor which if the price fall too much, you would rather hold the share then sell at this lousy price.