The SharePoint Site Collections report lists information about all of the site collections that are currently being reported on. The dashboard at the top of the page displays the total number of Site Collections, Sites, Document Libraries and Folders.
The Data Table lists each Site Collection, along with the date it was last modified, the item size, the quota used, and the quota available. The quota used includes items in the recycle bin and versioning.
Clicking a Site Collection will display more in-depth information for that particular collection. Selecting the different tabs will display information relating to the Site Collection's General Settings, Storage & Quota and Audit Settings.