The analytics on the overview page can be described as follows:
New Users: New Users are calculated by examining how many devices have downloaded and opened your app at least once in the time period
Addressable Users: Addressable Devices are the number of devices which have downloaded your app and opted-in/accepted push notifications.
Total Sessions: Is the total number of session during the set time period. A session is in progress when a user opens the app and starts using it until they close it
Unique Sessions: Unique Sessions is calculated from the unique users who open the app at least one time during the set period of time.
Mean Session Time: Mean session time measures the average amount of times users spent browsing within your app during the se time period.
Time Spent in App: The total time users spent within in your app during the set time period.