When you hit a creature with an attack roll, you can call on your mystical bond with nature to mark the target as your favored enemy by casting the spell Hunter's Mark.
You can use this feature to cast Hunter's Mark on a favored enemy a number of times equal to 1 plus your Wisdom Modifier, and you regain all expended uses when you finish a long rest.
Hunter's Mark does not count against the number of ranger spells you know.