Factions are different forces in the world of For Honor. There are three legendary factions, Knights, Samurai, and Vikings currently. Each faction originally had different roots and home, but now they compete with each other at the Blackstone Legion to restore their declined countries.
Class is a type of unit that player can control. Knights, Samurai, and Vikings have four different heroes and each of them belongs to one of the four classes: Vanguard, Heavy, Assassin, and Hybrid.