I think there is 2 types of haki. Normal haki and CoC haki.
You can use normal haki for armament or observation. You focus haki in your ears, eyes, touch, etc and then you upgrade your level in observation haki. Remember Usopp at dresrossa, he was focusing so much in his eyes, until there was some kind of aura and then could use observation haki see further. Or Coby, who was hearing all the war, and was in a traumatic state that he was concentrating to much on the sound until he had greater ears and observation haki unlocked, depends on what you are looking.
The same for armament, it is just haki, we learned that haki can be controlled in especific spots, so you can use it in your attacks, for defense until Wano, where it was shown that it can also go outside of the body, more control of haki, you can use it for internal attacks, etc.
So that is just normal haki, Rayleigh stated that it can be trained for anyone to use it, so there isn't no difference between in people, it just a tool and what you can do depends on you.
While CoC is an another layer, said to be the manifestation of oneself soul, so might always be just for external control like defense and power, and as normal haki, it will depend on the usage you give it, doing the same that CoA, but now, a new layer aka more powerful.