Your CNC is used to manage various parts of your site, Email is managed from the Email Manager, the File Manager can be used to upload files to your site as well as edit files directly on the server.
The FTP Manager is to create extra FTP accounts for specific use, many never create extra FTP accounts as they simply use the main FTP account to upload files. The MySQL Manager is used to create MySQL Databases which certain PHP based applications/scripts require such as WordPress.
In regards to using Kompozer have you worked through the tutorials located at the below link?
http://www.thesitewizard.com/getting...torial-1.shtml
-Bob