Skeletons are undead, ranged hostile mobs equipped with bows.
Skeletons spawn in dimly lit areas, and will burn in sunlight. When skeletons are nearby, their presence is indicated by the intermittent harsh rattling sound of their bones. Skeletons will chase any player they see within 16 blocks, and will climb stairs, navigate mazes, and traverse other complex obstacles in order to get within shooting range. When they are within 8 blocks of the player with a clear line of sight, they will stop chasing and start shooting the player with arrows. If the player moves more than 16 blocks away from the skeleton, it will cease pursuit.
Like zombies, skeleton burning occurs at dawn when the sun is 15 degrees or greater above the ground, unless the skeleton is either in shade, water, or wearing a helmet. If not wearing a helmet, they will attempt to find shade or water to keep from burning. Unlike zombies, which will always chase the player if they see one, skeletons will not exit the shade area even if attacking a player. Skeletons run from wolves, as wolves attack and chase skeletons. When skeletons are safe from sunlight, they will shoot at any wolves that attack it.
For more information, please see the Wiki website
Please also see the videos below about the skeleton: