A team is a group of agents that work can be handed to as a unit. It's a routing tool rather than a permission — worth being clear about, because the name suggests otherwise.
1
What a team is for — and what it isn't
Teams exist so that work can be aimed at a group instead of a person. When an automation routes a chat to a team, it doesn't just label it — it looks at who's in that team and hands the conversation to whoever is carrying the fewest open chats right now, which is how you spread load across a shift without anyone assigning by hand. Teams are also the lens in Analytics, letting you compare how support is doing against sales. What a team is not is a wall: it doesn't limit what anyone can see. Everyone on the account sees every conversation in Team Inbox regardless of which team they're in, so a team decides who work is pushed to, never who's allowed to look. If you need to actually restrict someone, that's a role, not a team.
2
Building one
Add Team takes a name, and that's deliberately all — members come after. Open the team again once it exists and you can pick who's in it; it catches people out the first time, so expect the two passes. One thing that isn't obvious: Administrators are in every team automatically and can't be taken out of one. That's usually what you want for oversight, but it has a real consequence worth planning around — because a team's members are exactly who round-robin picks from, every Administrator sits in every team's rotation and will be handed chats like anyone else. If your admins shouldn't be answering conversations, give the people doing the answering their own role rather than making them admins.