This book is part of the Torah – the first 5 books of the Bible. Sometimes folks will get ambitious and decide to read the Bible through, beginning with Genesis. If they make it through Leviticus, this book is where they often falter. The book begins with a census of the Israelites in the desert (hence the book’s title), and then follows them from Sinai to the plains of Moab and ends with the people beginning to prepare to invade the promised land.
The best story from this book, in my humble opinion, is found in chapter 22 and is usually entitled “Balaam’s Ass.”
Date
The oral tradition of this material is ancient, but it probably wasn’t compiled into written form until the exile or the return.