In the domain setup -> virtual paths, you'll be able to add/edit/delete virtual paths
Name: Name of the virtual path that will be visible in directories/folders.
Physical Path: The local physical path (drive based, ie: f:\path\, or UNC based, ie: \\computername\path ) to the virtual path/folder/directory.
Mapped Path: The location of where you want the virtual path to be displayed in directory listings.
%HOME% -- list the virtual path in the domain home directory.
%USER% -- list the virtual path in the user home directory.
In addition, the user will require permissions to any virtual directories you add in the user's properties.
Reminder: When running as a service, if the system account does not have access to the virtual path, it will need access to it also. Another option would be to change the Core FTP Server service user (service "logon" properties) to be the user that mapped the drives and/or a user with administrator rights.