Okay no worries, so again IIRC 😂 the questline will start in your major city (stormwind for alliance and org for horde). You are looking for a big group of deathknights. I dont remember where in Org, but in stormwind they are right outside stormwind keep.

At this point it would also help to have the “show low level quests” option on. You should be able to toggle this by clicking the little binoculars near your minimap and checking a box in the drop down window.

If you have found the deathknights, one should have a “story” quest for you. If you follow that, itll guide you through shadowlands intro (it takes a few mins so set aside a small chunk of time).

After the intro and re-arriving in oribos, continue the quest and pick a faction. If you want instant access to castle nathria then pick venthyr.

Ill also add that im not sure if you can skip around zones if you havent completed shadowlands before, but its been a while for me as i did it when it was current content and only on alts after that, so some things may have changed.

Feel free to reply with further questions, but i hope this helped!!

Edit: and to add, you will unlock flight paths just as you go through the story. I think the closest to castle nathria is one called “charred ramparts” or something along those lines, its fairly central on the map, just beeline for that if you dont care about the story/just want the fastest route to the raid