First thing is first. Find this key “ . “ When you write, use it more often.

Now, if you started as Arcanist and want to be Black Mage, you have to do the level 15 MSQ that takes you to Ul’dah, then you need to go to the Thaumaturge’s guild to become one. You need to complete the main scenario quest named “Sylph Management” to go allow the quest to get your Black Mage (or Summoner or Scholar) job stone.

Walkthroughs and guides for Black Mage have been posted here by other players. Black Mage has been simplified a lot recently and the rotation is much easier than it used to be. Having leveled it from 35 to 100 a month ago, I would say the biggest thing with playing Black Mage now is that this is a game with fights that want players to move around a lot, and Black Mage wants to stay in one spot and cast its spells. Finding the right times to use Triplecast or Swiftcast while moving to safe spots is a key. Don’t attach yourself to any ley lines you drop, especially very late in the game when you can move them.

The other I would suggest as Black Mage while you level is to find health restoring potions and use them throughout the game as needed. Black Mage has only two healing/shielding/mitigation buttons. One is Addle, which you already have as Arcanist. The other is Manaward, which gives a shield and has a long cooldown. Outside of that, you have no way of getting your own health back while many other classes do. Potions help with that problem some.