In Fantasy Grounds open Items, press Import (or type /twimport), paste, press Import. The item arrives as the Core module carries its own, with its Use button, coating or area where it has one. An item of the same name in the campaign is updated in place.

The record as the game's content/items.json holds it. The price is the tabletop's: the game keeps none, and the ruleset's price list (fgu/data/items_ttrpg.json) carries it. An item only the table uses goes in that file's own list.