Mob-skeleton

A skeleton is a very dangerous mob because when it sees you it will constantly shoot you with arrows.Like zombies, they spawn in the night / underground and burn during the day.

How to kill
Its best to get an enchanted sword and hit it with it. Also,you could use a bow from quite long distance.

Drops
A skeleton will drop bones, sometimes a bow and arrows, and very rarely some armour (sometimes enchanted) or enchanted bows.

Trivia
Skeletons, like most other monsters , can climb up ladders

Occasionly, they will be a spider jockey which is a skeleton riding a spider and is very dangerous.

If skeletons or in water, or have armour on, they won't burn in sunlight.