God sent Samuel to Bethlehem to find a man called Jesse and his 8 sons. He would decide which one of them will be the next king , after Saul was king.
When Samuel met the youngest son, David , God spoke to him and said " he is the one". He was the family shepherd.
The problem is with the Philistines was that they had many giants living in their village one their strong giants was called Goliath.
Goliath was covered with armour to protect him and carried a big spear. Every morning and every evening for days he shouted to the Isralites in his big deep.
When Saul and his men heard this they were very afraid some of the men were Three of the brothers They were the oldest brothers in the family who could go out there and fight.
So Saul dressed David in to armour and things like that and went off to fight in all his gear when he got to goliath he thought it was all a joke but it was not . he got out a stone and hit it so hard and it killed Goliath