a trailing stop is a moving stop loss that follows the price (in its intended direction)
if you buy a currency pair at 1.0020 and you set a stop loss at 20 pips under that, 1.0000, then your commerce will shut when the price hits 1.0000.
If instead you place a trailing stop of 20 pips to get the exact same buy order at 1.0020, then that is exactly what occurs. The tracking stop follows the price, when the price goes up 10 pips to 1.0030, then the trailing stop goes up 10 pips to 1.0010. When the price comes back down, the trailing stop does not change.
Basically...