In this chapter, Joshua allots the inheritances for the three tribes that live east of the Jordan.
This chapter begins with the LORD listing the territories that Israel was promised, but "remains to be possessed". The lands he lists are the territory of the Philistines (along the coast, extending through Gaza up to Ekron) and several territories near Sidon and Lebanon, which is the northwest and northern territories largely corresponding to modern-day Lebanon. This is pretty much exactly what I wrote two chapters ago when I said that the territories conquered did not correspond with the whole land that was promised.
What the LORD says in v. 6 and 7 is basically that Israel won't conquer this land during your lifetime, Joshua, but I want you to apportion the land as if it were already won and then Israel can go conquer it later. There is an obvious triumphalism about this, dividing up land amongst the tribes even before it's been captured, but I'd like to focus on a more practical implication, which is that this creates an inequality between the tribes that are assigned land which has been captured versus the tribes that are assigned land that has not been captured. The tribes given land from the Philistines or Sidon will have to either fight for their inheritances or find an alternative place to live, outside of their allotted land. This is an issue that will show up again in the book of Judges.
In vv. 8-14 we are given an account of the territory east of the Jordan given to the two and a half tribes (what I sometimes call the Transjordan tribes). There are various borders listed which, again, I do not know much about, since it doesn't really affect the flow of the story or the general narrative. One thing that is worth mentioning is that v. 13 talks about two tribes that were not fully dispossessed. Normally this is a bad thing for Israel because Israel was commanded to destroy all the nations in the promised land. In this case, it isn't so bad because they are trans-Jordan nations and therefore outside of the promised land. It was only by accident that Israel conquered the two nations east of the Jordan, so there is no prohibition against Israel making peace with the Geshurites or Maacathites as per Deut 20.
V. 22 contains a note that the Israelites killed Balaam, the prophet from Num 22-24, who was called to curse Israel but blessed them instead. He was held responsible for the idolatry in Peor that occurred in Num 25, and this is the second time we have been informed of his death (the first was Num 31:8, 16).
The rest of this chapter is basically just a detailed account of the territory of the Transjordan tribes. All of the naems of cities and rivers and valleys is pretty confusing, but the general idea is that Reuben is the furthest south, along the eastern border of the Dead Sea, and including Beth Peor which is one of the places that Israel camped when they were coming up from the wilderness. Gad is also east of the Jordan, north of Reuben, extending up to the Sea of Galilee along the Jordan. Manasseh has the territory of Bashan and half of Gilead, which is east and northeast of the Sea of Galilee, corresponding to the modern-day Golan Heights. There's a bunch of cities listed, some of which have been located and some that haven't.
But I think this should give my readers some idea of the size of the eastern territories. The three Transjordan tribes have essentially as much territory as all the other nine tribes put together, and that's because the Transjordan tribes have a lot of livestock which requires a lot of grazing land. This was part of the calculus that went into their request in the first place (Num 32).