Slay The Spire features a rather impressive selection of various buffs and debuffs that players ought to familiarise themselves with, and fast, because the game doesn't skimp out when it comes to dishing them out left and right.
Somewhat counterintuitively, Artifacts are no different than, say, Poison, or Bleed debuffs in Slay The Spire. Since the game places a rather significant focus on maintaining and balancing the various buffs and debuffs that are being thrown at you and your enemies all the time, there was a need for a neutral, nullifying debuff too, and Artifacts serve that purpose.
In other words, each stack of Artifact can block one application of a debuff such as Weak, Vulnerable, Poison, etc. which makes it practically a must when facing status-modifying enemies. There are various ways of attaining Artifacts such as cards, relics, and events, but keep in mind that enemies will employ them, too.
Slay The Spire is coming out on Steam, on 23rd of January, which is this week. If you're interested in buying the game, you might want to do so before the 23rd, as the base price will rise as the game leaves Early Access.