Trailing stop-loss is different then a normal stop-loss setting. With normal stop-loss if you set the percentage to 6%, the currency will be sold with a loss if it made more loss then 6%. With trailing stop-loss it will keep track of the price move the stop-loss rate upwards when the price of the currency goes upwards. So if you set the trailing stop-loss percentage to 1% you will have a stop-loss of minus 1% of the highest rate it reached. So if the currency moves up 10%, the stop loss will be at 9% profit. With trailing stop you can lock in your profits much better. 

Arm trailing stop-loss 

If you only want to let the stop-loss trail up when it is going to make a profit, then you should enable arm the trailing stop-loss at a certain percentage. The arm trailing stop-loss setting is for when the trailing stop-loss should start trailing, for example when the price is 2% up.