It's no secret that Naadam is hard on squishies. Since a lot of new players will be there very soon, a handy guide is needed, and I couldn't find one. So here's my take, and I invite smarter readers to improve on my advice.
You can encounter Naadam at level 66 and it's capped at level 68. Many squishies will find it too hard at 66, and very hard at 67. You certainly need the best gear to have a chance; food and health potions are also helpful. As a BM, I needed Manaward and Scathe on handy access, along with a robust rotation that would accommodate a lot of running around. The mechanics should be familiar to you from Main Quest instances you've completed.
Part 1 – Getting There
Follow Hien and dismount when he does. Focus down the mob who's shooting at you and the one that's shooting at him. Follow him on foot when he heads south. Rinse and repeat with the second set of mobs. You will soon see the magic circle called Oovo. Don't go in!
Part 2 – Capture the Flag
You'll be encountered by three groups of three weak mobs. Some AOE is useful, or a couple of Fire IV hits each. That clears you a path into Oovo, where you right-click to channel attunement, which will be interrupted by a cutscene where you meet the two bosses who'll be making your life very interesting very soon.
The big guy (Magnai) will be all over you with a couple of his friends. Target his friends first and watch out for his AOEs.
KEEP ONE EYE ON OOVO AT ALL TIMES. It's easy to see when somebody else is attuning there; hit them once with Scathe and forget about them!
The mean little gal (Sadu) will soon bring her friends to the fight while you're hitting Magnai. She's not much of a threat until she conjures up a couple of masonry monsters (the Stellar Chuluus) that must take priority over everything but protecting Oovo.
After you kill the Chuluus, finish off Magnai and Sadu, dodging some nasty AOEs. That should open your way to finishing attunement with the Oovo, and the hard part is done!
Part 3 – Comic Relief
An old friend shows up with his buddies and makes big talk. Your main task is staying alive until Sadu can complete her Chuluus again. You'll see an ominous count-down which is just the number of seconds you need to stay alive to finish the duty.
Congratulations! You're ready to pick up your last Aether Current from Hien and get airborne.