David was a person who really had faith that God loved him and that God would help him whatever he asked him to do. David loved to sing to God and he wrote lots of wonderful songs about Him. He loved to play music to God too, and praise Him for all His wonder and power. He especially loved to play the harp.
One day when David was looking after his father's sheep, a great lion came along to steal and eat one of his sheep. David shouted to God to help him, and ran towards the lion, calling "Leave my sheep alone, lion!" Perhaps he used his sling and a stone from his bag, a bag he kept filled with lovely strong smooth stones from the stream. He took his sling, whizzed it round his head and zoom! Clunk! it hit the lion between the eyes and if collapsed, and fell in a heap on the hillside. Perhaps David finished him off with a knife, or a stone. God gave him the faith and the strength to kill the lion. No wonder David wrote songs to praise God for helping him.
One day a bear came to steal his sheep, and again, with God's help, David killed him! David's faith in God increased day by day. One day, David's father sent for him. "I wonder what father wants?" David must have thought. He ran home and hugged his mother and father, happy to see them again. "I want you to take some corn and ten loaves of bread for your brothers, and ten cheeses for the captain to share out with the other soldiers who are fighting in the army against the Phillistines" his Father said to him. David had seven brothers, and all his brothers were older than him. The three eldest brothers were fighting for the great King of all Israel, King Saul. David was excited. This was different from looking after the sheep.
David ran, with the bread and cheese all the way to where the battle was being fought. It must have taken him a few days to get there, as the battle was being fought about 30 miles away from where David's family lived. When he arrived, all was quiet. Whatever was going on? David expected to hear cries and shouts from the battle field. He found his brothers, who were sitting, and not fighting at all." David found his brothers on the mountainside where all the soldiers belonging to King Saul of Israel were camped. The Phillistines were all camped on a mountain opposite, and there was a big valley in between the two mountains. Suddenly, there came a shout from the valley below. All the soldiers in the valley began to run. The Phillistines had a giant called Goliath. He was over seven feet tall, and he was very scary. He challenged the Israelite army to a duel with their strongest man. Everyone was afraid of him. All the soldiers trembled and shook at the thought of fighting such a fierce and strong warrior. David wasn't afraid! He spoke up and said, "Who is this unholy Phillistine! How dare he fight against the armies of the Living God!" Eliab, David's brother was angry with him and told him to get back to his sheep, but someone ran and told King Saul what David had said, and he sent for him.
David told the King he would fight the giant. When King Saul asked him why he wasn't afraid of him like all his warriors, David told him about the lion and the bear he had killed, and that he would treat the giant just the same! He said that just as God had helped him kill the wild animals He would help him now to kill the Phillistine giant, Goliath. King Saul wanted David to wear his armour, but of course he wasn't used to wearing armour, and David just wanted to trust God to help him. So, with his staff in his hand and with his sling and five smooth stones in his shepherd's bag, he set off to fight Goliath. When Goliath saw him and how young he was, he laughed. "Come near me and I will feed you to the birds and the beasts!" he shouted. Then David cried out, "You come to me with a sword and a spear and a shield: but I come to you in the name of the LORD of hosts, the God of the armies of Israel. This day the Lord shall deliver you to me, and I will kill you, and take your head from you, and I will give your body to the birds and the wild beasts, just so that everyone will know that there is a God in Israel!" The Phillistine began to come near David, and David quickly put a stone into his sling and threw it at Goliath, hitting him on his forehead. Crash! down he fell! David ran and took Goliath's sword and killed him. He then cut off his head!

Here is one of David's songs. You can read it for yourself in the Bible, in Psalms, Chapter 18, verses 1-3.
I will love You, oh Yahweh, my strength.
Yahweh is my rock, and my fortress,
and my deliverer; my God, my strength,
in whom I will trust; my buckler,
and the horn of my salvation, and my high tower.
I will call upon Yahweh, who is worthy to be praised:
so shall I be saved from my enemies."