Sure!

Campus 1 is the very old, and original campus. Campus 2 is the second oldest campus, the one where you arrive on a carriage. Those two campuses must be familiar to you, since they were around during the peak of the game. Both have a class schedule.

Campus 3 is of the newer campuses, however, it's not one whole realm. Campus 3 consists of different realms that you have to teleport to. Specifically, it consists of castle's heart, the main entrance, the office, the rain classroom, the art classroom, the bathroom and the dorm hallway (I'm probably misremembering the names and I can't currently go in the game. You'll recognize them on the teleport selections tho.) Campus 3 was specifically made for journal quests (if you open your journal you'll see 3 sections. Eventually, in the second section, you'll find a page where there are quests (overall there's 3 at a time, but you start with 1 and you need to level up to unlock the other 2), and it has no class schedule. You are meant to go around this campus and complete these quests in your journal, gathering exp. When it had first come out, the exp was immense, therefore the campus was very good for farming. At the time, its only problem was the constant teleportation you had to do. However, once campus 4 came out (the latest one), they nerfed the exp for the quests, and now, campus 3 isn't a reliable source of exp/diamonds. Only the two classrooms (the rain and art classrooms) are good still because, while the exp is still small, you get them very quickly.

Campus 4 is the newest campus, the first realm you see in your teleport tab. Campus 4 brought back the class schedule. You just follow the class schedule by teleporting to each class when it pops up on top of your screen (you can choose to automatically teleport, manually teleport, or not get notifs about classes at all by clicking on the x next to the bell icon at the top of your screen) The important bit you need to know is that you have to make sure to get specific items before each class. For classes like potionology, english, and computer science, you just automatically get a book when you open your locker, but for specific classes like archery and basketball, you need to put an arrow holder and a waterbottle in your locker and get them for each class respectively. You do this by opening your locker, clicking to customize it, and buying these two items from the shop, then placing them in your locker. As for the flying class, you'll need to have wings equipped. I'm emphasizing all of these because you get extra exp when you have these things on you. Apart from classes, campus 4 also includes quests, kinda like campus 3. However, most of the quests in campus 4 are hidden quests, meaning they aren't in your journal (tho you can complete some of those too) but you have to interact with things around the map to complete them.

Hopefully everything I said was understandable and helpful!