SignIn into Graph Explorer to get folder and file details, here is the graph explorer URL: https://developer.microsoft.com/en-us/graph/graph-explorer
Get UserID
https://graph.microsoft.com/v1.0/me/
Get Calendar ID
https://graph.microsoft.com/v1.0/users/1465xxxx-xxxx-xxxx-xxxx-xxxxxxxx1f54/calendars
Access another user calendar
There are two scenarios where an app can get another user’s calendar:
If the app has application permissions, or,
If the app has the appropriate delegated permissions from one user, and another user has shared a calendar with that user, or, has given delegated access to that user. See details and an example.
Get Group ID
https://graph.microsoft.com/v1.0/groups
Note: Microsoft Graph API can not get outlook/masterCategories of other users.