is where you place your web files. Anything you place in this folder will be viewable on the web.
is the same as public_html. Yes, it's a bit confusing, but the www is what is known as a symlink, which is a link that leads to a real directory or file. In this case, the www symlink leads to the public_html directory.
contains all your stat files for webalizer, analog, and awstats.
mail and etc :
contain mail and it's various configuration files.
is used if anonymous ftp is enabled
_vti_bin, _vti_conf, _private, etc are all part of Front Page extensions. If you don't see these, don't worry, it just means FP extensions haven't been installed for this account. If you wish to install them, please open a ticket, and we will install them for you.