The Book of Ruth is a beautiful story. It is in the Old Testament part of the Bible.
The Book of Ruth is about a young widow, Ruth. Ruth was a foreigner. But she came to Israel to help Naomi. (Naomi was Ruth's husband's mother.) Ruth left her own gods, to serve the real God. Naomi and Ruth were very poor. But Ruth could collect any grain that remained after the harvest. This was God's law. And one man who respected this law was called Boaz. So, Ruth came to Boaz's field to collect grain. Boaz saw Ruth and he loved her. He agreed to pay her family's debts, so that he could marry Ruth.
Ruth was just a poor foreigner. But her family became Israel's royal family. Both King David and Jesus belonged to this family.