Step 1:
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
Step 2:
Get UserID
https://graph.microsoft.com/v1.0/me/
Step 3:
Get Root Folders
(replace UserID with your userId that grabbed from previous step)
https://graph.microsoft.com/v1.0/users/UserID/drive/root/children
Get Folder Items
(replace UserID and FolderID with yours that grabbed from previous step)
https://graph.microsoft.com/v1.0/users/UserID/drive/items/FolderID/children