Vol’Dun is the hardest and most tedious of the Horde Zones in Battle for Azeroth. It’s also probably the one that makes the most sense. Each sections of quests leads directly to the one you should do next. For all of these reasons it’s going to be best to get this one done early. Thanks to any legendary items you might have collected in Legion, you’ll be strongest in the leveling process before 115 and weaker after — because that’s when the legendary effects stop working.
Island Expeditions are a new idea that digs into the island vibe brought in by Battle for Azeroth and allows players to team up in groups of three to venture out onto various islands to gather all-important Azerite while fighting against enemies on the island and completing quests. The twist is that Island Expeditions are also a race against the opposite faction — whether it's three AI characters or three real players is up to you — but you may have to do a little player vs. player (or fake PvP) if you happen to run into them.
Congratulations on reaching Level 120! There are a myriad of new things to do. The first thing you should do is head to your faction hub ship where you have been doing your mission table quests and footholds to pick up and complete the quests necessary to unlock World Quests. World Quests will provide you an opportunity to grind reputation levels, acquire gear, and gather Azerite. There are tons of new things to do that we will cover in our Level 120 Battle Guide found here: Level 120 Battle Guide