You can see the member list for a team and channel(s) are open to the entire team. 

See this support article from Microsoft Support for instructions: https://support.microsoft.com/en-us/office/see-who-s-on-a-team-or-in-a-channel-5c6be9be-9c45-4a0f-a1a0-f332b23cb6b7?ui=en-us&rs=en-us&ad=us

Related articles

Related articles appear here based on the labels you select. Click to edit the macro and add or change labels.