In this chapter, the LORD instructs Joshua to lead the people into the promised land.
This book leaves right where Deuteronomy left off. Moses is dead, Joshua has been anointed leader of the people, and the nation of Israel is encamped near the eastern bank of the Jordan. Joshua is instructed to lead the people into Canaan, and he takes this as an opportunity to remind the tribes of Reuben, Gad and half of Manasseh (henceforth the Transjordan tribes) that they promised to go to war along with their brothers (this promise occurs in Num 32).
I think there are two notable characteristics to this chapter. The first is the recurrence of the phrase "be strong and courageous", which is first stated three times by the LORD, and is later repeated by the Transjordan tribes when they are assuring Joshua that they will go into the promised land. When I previously discussed the overthrow of Sihon and Og, who were two Amorite kings slain by the Israelites, I said that these were important examples that would be used to encourage the Israelites, and I also said that morale is a huge component of ancient warfare. In this chapter, we see a similar theme in the phrase "strong and courageous", because the LORD is trying to encourage Joshua to stand strong in battle and Joshua basically passes that encouragement down to his men.
The second notable characteristic is how obedient and responsive the men from the Transjordan tribes are when Joshua commands them to fight. In light of the prior rebellions of the Israelites during their wandering years, we now see that the Israelites are being largely obedient again. This pattern of obedience will last through most of Joshua with only a few exceptions. It's only towards the end of the book and into the book of Judges that the Israelite rebellions start becoming more widespread and more severe. During Joshua's lifetime, the nation will be predominantly aligned with the Lord and the covenant.
Other than that, I don't think there's much else happening in this chapter. Joshua reaffirms the deal that Moses made with the Transjordan tribes and Joshua tells us that the people will depart within three days (possibly recalling the three days of preparation before the LORD descended on Sinai, Ex 19:11).