Operate is an action used on items. The operate function is only usable on an item that is equipped.
Operate usually only works on items that are either enchanted, non-tradeable or quest-related like the following:
What it works on
|Enchanted items||Non-tradeable items||Quest-related||Special items|
|Combat bracelet||Explorer's ring||Reindeer hat||Cape of accomplishment|
|Amulet of glory||Ava's accumulator||Chocatrice cape||Skull sceptre|
|Games necklace||Karamja gloves||Broomstick||Chocatrice cape|
|Ring of duelling||Falador shield|
The action 'Operate' still exists on some items, but some have been changed from rub or operate to something more specific. Take, for example, an Amulet of glory. When right clicking the amulet, while being equipped, it lists the destinations instead of the usual "operate". It would also be possible to right-click any other worn equipment, such as a platebody, you would receive the message: "You can't operate that."
Also, if you wear something with way to operate(for an example, golden hammer), then switch something for it's spot and right click and select something you could have done with previously worn item, there appears text: "There is no way to operate that item."
In certain quests and occasions, you may have to operate a machine or sceneric tool. E.g. in 2008's Easter event when you had to operate the incubator.