What can be done with artifact clothes?

You can assign artifact clothing to be worn by a particular dwarf through the military menu. Don't think it works for jewelry.

Artifacts cannot be sold in Fortress mode, but if you put them in containers of sufficient weight (lead, gold and platinum are great for making such containers), the containers will remain in place after abandoning the fortress, allowing you to easily retrieve them with an adventurer. If you install a display case mod (a world regen may be necessary), you can use artifact jewelry and such to boost room value by putting them on display.

Only weapon and armor artifacts can be effectively used by your dwarfs. Clothing and crafted goods artifacts only add to your fortress value.