Neverwinter's Shadowmantle module, Cryptic's put out a clear-cut guide to what's what with these special objects.
Artifacts are items that imbue the possessor with certain bonuses while at the same time giving players new skills to use. These skills recharge every few minutes and offer significant benefits, from healing to damage boosting to... shopkeeping. Players will get their first artifact for free at level 20, after which additional artifacts will need to be found elsewhere in the game.
Artifacts can be leveled up through the refinement system (also coming with module 2). Ultimately, a player can have one active and two passive artifacts slotted at any given time, with the passives offering only the stat bonuses.