Click "Refresh usage stats". This may take some time, depending on the storage used and number of files/e-mails.

Once completed, the usage shows where your files go to. The *Web* value indicates all files available in the File manager, excluding the logs files. 

Mail represents all e-mail accounts. Please note: when you delete an e-mail, please also clear your bin. Otherwise, e-mails remains stored. Deleting e-mails only helps when you are using the IMAP protocol for fetching e-mails. POP3 stores e-mails locally, and will not make more space available on the server.