The Book of Ruth is the eight book of the Bible. It is unusual in that it does not explicitly discuss miracles, prophets, national politics or conquest, or moral commandments. Instead it is the short, simple story of a Moabite woman, her Jewish mother-in-law, and the man she seduces in order to escape poverty. It appears that this book was included in the Bible largely because Ruth is claimed to be a great-grandmother of David.
Naomi's husband Elimelech and her sons Mahlon and Chilion die while their family is living in Moab. Naomi decides to return to her home town of Bethlehem, which her famine had left during a famine years previously. Of her Moabite daughters-in-law, Orpah returns to her people, but Ruth accompanies Naomi, whom she loves very much.
Ruth, being without a husband or father to rely upon, goes out into the fields to gather the leftovers during the barley harvest. Boaz, the owner of one of these fields, takes notice of her and encourages her to come to his fields to gather and to eat some of his bread. Ruth returns to her home with Naomi, who tells Ruth that Boaz is one of her relatives (since widows are rarely virgins, one of their only ways of remarrying at this time would have been to find a man from their dead husband's family to marry).
Naomi encourages Ruth to improve her lot by marrying Boaz, and tells her how to seduce him. She sneaks up to him, waits for him to eat and drink and go to sleep, then sneaks up to him and uncovers him. He tells her to stay the night with him, but that she has a closer relative that he will have to check with before taking her for a wife. In the morning Ruth brings a present of barley back to Naomi.
The closer relative that Boaz mentioned wants Elimelech's field, but doesn't want to take Ruth as a wife, in part because he's concerned about the inheritance of his other children could be threatened by any children of Ruth. He then gives Boaz his shoe because that's the customary way of displaying that he has handed over any rights to Elimelech's stuff. Boaz therefore buys Elimelech's property from Naomi, including the daughter-in-law Ruth. Ruth has a son, Obed (David's paternal grandfather), whom Naomi nurses as her own.