Manage app setup policies in Microsoft Teams - Microsoft Teams | Microsoft  Docs


Activity: Shows you the most recent notifications 


Chat: Where you can reply to recent messages or start your own chat


Teams: Where to access the relevant groups that you are a member of – including all shared documents and dialogues


Meetings: Shows you your Teams calendar.  You can join meetings or schedule your own meetings from here


Calls: You can use this outside of scheduled meetings to contact users in your groups

Files: Shows you the recent history of files you have viewed/accessed/edited in Teams as well as any downloads