Trailing Stop is an kind of stop loss. This function enables you to automatically set stop loss level whenever the profit you got has exceeded the minimum trailing stop level. If the profit has not exceeded minimum trailing stop level, it will not work !
Please keep in mind that trailing stop usually is executed directly from your computer (client software), not your broker's server so it is highly recommended to put a stop loss besides trailing stop.
The objective of trailing stop is to protect your profit if the market moves against your position so the profit will never go anywhere.
If Trailing stop level is set to 10 pips. Right after your position has reached profit more than trailing stop level (more than 10), then the stop loss will be set to 10 pips away from your open position to protect your profit . Lets say you have already got 10 pips profit, then trailing stop will put a stop loss to 0 (10 pips away from open). If your profit is 20, then stop loss will adjust the stop loss to 10 points profit (still 10 pips awa from open).
Trailing stop = 10 pips, You open a buy position at 1.2000, suddenly price moves to 1.2010, trailing stop set a stop loss at 1.2000 (Break Even). Market keeps moving to 1.2020, trailing stop level will be adjusted to 1.2010 (10 pips profit), and so on.