Incursions are a new world content activity that are unlocked when one character has unlocked World Quests. This feature is unlocked account-wide meaning that all characters on that account can access Incursions even without being Level 120. This provides for a lucrative experience acquisition method that is available in a similar pattern to what Legion Invasions offered with nearly an entire level earned by completing an Incursion series which involves four World Quests and one mini-scenario at the end. These also grant item level 370 weapons and Azerite armor, so they should be done any time they are up. Incursions follow a similar schedule to Invasions and are available for 20 hours once they are initiated.
If you’re jumping back in for Battle for Azeroth, we recommend checking out the big “what to do first” guide from Wowhead. You’re also going to want to brush up on specific advice for your class—both Icy Veins and Wowhead have incredibly detailed guides for all of the game’s combinations of classes and specializations. Make sure you go in and figure out all the new (or changed) talents you’ll be using, and start to memorize a typical combat rotation so you don’t die nearly as much in game’s latest incarnation.