When your items are in need of repair, or when looted items need to be ‘restored’ you can purchase this box from any NPC crafting guildmaster.
The default setting for the box is ‘blacksmith’, if that is not the correct repair type select from the box’s context menu the repair type you need and place your items in the box, or select ‘Fill from Container’.
Select from the context menu again and target the crafter you wish to undertake the repair. This will open a trade window which shows a repair contract document. Enter the agreed sum into the box in the trade window and click ‘accept’, the crafter will also click ‘accept’ and the repair is done. You can then select from the menu ‘Empty Contents To Pack. At no time do the items being repaired leave your possession.