The book of Joshua tells us that Joshua was commissioned by God to lead the people into the promised land. We learned how Rahib hid the spies Joshua sent into Jericho and how her and her family was spared when Jericho was destroyed. It also talks about obedience and the importance of obeying God completely in the story of Achans disobedience.
Joshua also divides the land amongst the 9.5 tribes that crossed the Jordan. the other 2.5 tribes settled on the other side of the Jordan.
Also, in Joshua it explains that Joshua took control of the entire land and there was rest from war but there was still areas that needed to be conquered. So basically they only needed to finish what they had started. The lesson explains the same is true in our lives. Satan is defeated when we accept Christ we only need to go ahead and possess Christs blessings for ourselves. It is our choice.