This report shows the storage history of your Site Collections. The size of your Site Collections are tracked daily and measured in Quota Used as Megabytes (mb) or the percentage used of the storage quota set.
The date picker on the top right corner allows you to customize your view by choosing the start date and end date.
You also have the option to filter your view by choosing specific Site Collections to view. Simply highlight the Site Collections you want and click Apply.
The table at the bottom give a daily breakdown of Quota Used (GB), Storage Quota (GB) and Quota Used (%) for each selected Site Collection