https://www.youtube.com/watch?v=sLhJmNoZTsY

This is one of the videos teaching SMN rotation..

There two type of Skills for both Disciple of War (DoW) and Disciple of Magic (DoM) Classes or Jobs, namely Weapon Skill (DoW) or Spell (DoM), example for Arcanist skills are Ruin, Bio, Miasma, etc., and the second one is Ability, for example Addle, Break, Drain, etc.

https://ffxiv.consolegameswiki.com/wiki/Arcanist

each share different Cooldown (CD) time. I think they like to call the Weapon skill and Spell cooldown with the term general/global cooldown (GCD)..

So, when your Spell/Weapon Skill is under GCD, you can cast the Ability.. A good understanding of the two will result in maximized damage..