Trigger orders allow you to mark points when there is a desire to buy or sell. As soon as a trigger order is on the border or inside the spread, it will be converted into an exchange order.
To place and withdraw trigger orders, you need to switch to the trigger orders mode in the DOM menu. 
Enable / disable trigger orders mode
The left mouse button places a trigger order to buy, and the right one to sell. Double-clicking with the left mouse button on a trigger order volume removes this order. The space bar removes all set trigger orders. The placed trigger order can be rearranged using the mouse.
The Margin for the trigger order sets the maximum slippage when triggered. To set up slippage, in the DOM menu select Settings and options → DOM parameters.
In the window that opens, on the Trading tab in the Margins section, enter the value of the margin in the Trigger orders field (in price steps, not in points). As soon as the price reaches the trigger order marker, the position will be opened on the market, but the market order will be sent to open the position with the specified maximum slippage.
If the condition is not met, after the specified slippage value (in price steps, not in points), a limit order to open will be placed and the position will not be opened until the price returns to that specified by this limit order.
