Short answer
HubSpot's KB: create skills such as languages or custom skills, assign them, then add routing rules per connected channel. Teams and users are optional, so you can route on skills only. A skill can't be deleted while assigned. Skills apply to Service Hub Enterprise seats.
1. In HubSpot
The relevant screen in my demo portal.
2. Worth knowing
Start with languages; they're the easiest skills to define.
3. Related
Ticket routing and availability.