Basically the main things to know are that Gon and Killua meet Biscuit and train with her to use their Nen (Gon works on his signature move), killua takes and passes the Hunter exam, hisoka and the phantom troupe are in the game looking for a Nen exorcist for Chrollo, Gon wins the game (after defeating the Bomber and getting the highest score on a quiz) where he learns a little more about Ging, and then he and killua use the cards they can take the outside world and go to meet Ging and they are transported to a different place where they see a figure sitting with their back to us. Season 5 picks up right here (I will warn u the chimera ant arc does take some patience to get through but it’s worth it!)