You can assign descriptions to operands:
When you place them in the Ladder. When you place a Ladder element or function on a net, the Select Operand and Address dialog box opens, allowing you to enter a description.
By double-clicking an element that is already in the net to open the Select Operand and Address dialog box and edit the description.
By entering a description in the Output Window (Operand tab). In this way, you can assign a description to several operands at once.