Welcome back!
You are most confused because this is the most confusing set of systems and unlocks Blizzard have ever developed. Their new designer, Franz Kafka, is due a bonus.
Follow Korthia ONLY until you get The True Maw Walker, so that you can mount in the Maw. Korthia is good for nothing else at this point.
Renown 45 is when you get flying, so anything you would like to do for Renown is good. Covenant Campaign is good- two birds with one stone. Torghast is efficient, with one Renown per clear. A dungeon will give you at least one Renown. Daily Callings will get you a Renown. Just settle in to some routine for keeping your Renown coming in for a couple of weeks.
As Robokiller said, Zereith Mortis is where you want to be ASAP. It’s the Land of Milk and Anima - and also more Renown. Think a botched version of the Timeless isle, with earned flying, and a campaign to work through for a Legendary. Once you get on the right road, it does carry you through in a straight line pretty well. You should have the quest Call of the Primus in your log somewhere. That’s the one to follow.
I’m not aware of a video, but here’s a guide: https://www.wowhead.com/guides/zereth-mortis-activities-how-to-unlock
Your gear isn’t that far out of date, but if you feel the need to beef up you will find item level 229 Cloth Greens and a 229 Intellect Staff and rings, cloak, and neck on the AH. Prices vary, but they are usually reasonable.
Just get on the Zereth Morits train, do your Covenant Campaign, and things will start to make a little more sense. Well, not the story, and now I think about it not the worldbuilding or the characters, or … but, well, you’ll get more used to it. 
Ask again if you need more!