This shows the number of messages waiting in this user's Inbox. If you click on the number, you can see/manage the messages in the user's Inbox. The waste-bin icon to the right of the number, lets you quickly delete all the messages in the user's Inbox. The messages are deleted permanently, and cannot be recovered.
This shows the total size of the user's mailbox. Note that this includes other webmail/IMAP4 folders than the Inbox, so it is possible for the Inbox message count to be zero, but the mailbox size to be non-zero.
This shows any comments you have specified for the user.
Users have the following tabs in their settings window: