How to generate a SharePoint Inventory Report?
Perform the following steps to a generate SharePoint Inventory Report:
Select SharePoint Online Reports from the available vertical tabs. Then from left pane of the application, select Inventory.
For demonstration purpose "List General Settings" report has been chosen.
On selecting "List General Settings" Report, a pop-up window is displayed as shown below to select the scope of the report:
 

     
Once the data collection process gets completed, the report data will be displayed in the window as shown below:
 

     
Columns to be displayed on the Grid can be selected from the dropdown. By default, all columns are displayed.
 
After selecting the desired column from the dropdown, Click Refresh button.
 
Follow the above mentioned steps to run other Inventory Reports.