Mockingjay help.................?

Ok. After "The in" part 3 of Mockingjay, I got super confused. What the heck is going on? Why did Katniss say that "they're going back into an arena". Did the capitols peacekeepers basically set up an arena, that the teams/rebels had to get through to inate snow? Just please explain it. Whats up with the pods, and all that other crap.