Microsoft provides some Teams Usage reports in the Teams Admin Center (Note the Skype word has been removed from the title of this Admin Center) under the “Analytics & Reports” section:
Teams user activity.
Teams device usage.
Each Report displays information for the last 7 or 28 days. For instance, the “Teams usage” report shows information about the total active users, Teams & Channels active users, Active channels and Messages:
Note also that bellow the visual reports, there is also a grid detailing the same information but on a per Teams basis: