How can u use a custom model as an npc?

I would like to make an npc with a custom model, one with for example ribs. This would mean it exists out of a lot of parts, unions, etc. But I don't know how to correctly implement these into an npc. This npc needs to move too, but I already have scripts for the A.I. I just really wanna know how you could use that custom model as a (moving) NPC. Any help is appreciated.