Okay I will make it as simple as possible as I too found the IG guide confusing. The simple expalnation is you have two settings, "Distance" and "Step".
"Distance" is the figure you put in you want your stop to be just like a normal NT order. But as it is a "Trailing stop" it keeps that "Distance" from the current price on a gain +/- , but does not drop if the market turns against you. So locks in profits or limits losses.
"step" is like a notch on a one way ratchet. You set this to what you want the market to travel in your favour before before the ratchet clicks up another notch and locks in profit.
For NT orders above +30 pips after 8am I usually set it to "Distance" = 30 , "Step" = 10.
So for example today. Sell 15009. Once it got to say 14975 (+34) if you have set up a trailing stop on my figures above what would happened after you submit ther ammended order would be the stop would have trailed to 30 pips away from the current price (distance), rounded to the nearest 10 pips (step).
So @ +34 pips (14975) it would mean the trailing stop would adjust 30 pips from 15039 (NT) to 15009. This means the trailing stop has now adjusted you lock in break even.
Now once the market moves another 10 pips as it did to 14969 the 10 pip "step" will click up another notch and move the "distance" trailing stop to 30 pips away from 14969 , so it the stop will become 14999.
This means +10 pips is locked in and even if the market completely retraces to a normal NT loss you will get stopped out for +10 pips.
You can obviously set distance and step to what you like subject to lower limits of the trailing stop but remember the lower thay are, the quicker you may get stopped out if the market bounces back before carrying on in your favour.
It's swings and roundabouts. I don't use it to try and lock in profits to the max as you could often get stopped out too early and the nT carrys on to a bigger win.
I use mine to ensure that after 8am, if we are above +30 I can't go to a loss in the last 1/2 hour and could at least also lock in 10 pips, or hit the max 50 pips.
M