Darkness counts as anything from a forest at night to pitch-black caves, caverns, and windowless interior spaces. Use your judgment as Game Master to decide what counts as darkness.

A character in darkness can’t see and gets Disadvantage on all Attack Rolls and Ability Checks involving sight. Anyone with Darkvision attacking a person who is blinded by darkness gets Advantage on their rolls. Advantage is when you roll two dice to make a check and choose the higher roll. Disadvantage means you roll two dice and choose the lower total.

Darkvision

Darkvision lets a player or monster see in the dark. It’s not perfect. They can only see 60 feet as if in a hazy fog, and there’s no color, only black and white. 

Creatures with Darkvision sneaking up to attack another creature blinded by darkness? The creature with Darkvision gets Advantage, and the person blinded by darkness would get Disadvantage on any Saving Throws or Ability Checks!