Let’s understand it with an example, A buy order of EUR/USD is placed at 1.1443 and trailing stop is set at for every 200 points that the price moves up, the trailing stop would also move up 200 points. If the price moves up 200 points, the stop loss will also move up 200 points. But if the price starts to fall, the stop loss doesn’t move.
In this above example, 1 lot of EUR/USD trade is entered at 1.1443 with 200-points trailing stop at 1.1423. If the price then moves up to 1.1473, the trailing stop would move to 1.1453. At 1.1473, the trailing stop would move to 1.1453.
If the price then moves back down to 1.1463, the trailing stop would stay at 1.1453. If the price continues down and reaches 1.1453, the trailing stop-loss order would be converted to a market order, and you would be able to exit the trade at about 1.1453 thus lock in 100 points profit.
The same works even for a short trade except that you are expecting the price to drop, so the trailing stop loss is placed above the entry price.