How to determine the path to your home directory
Your "home directory" is where the directories that store all your other files are kept. It contains, amongst other things, the "htdocs" directory, which is where the files for your website are stored. When you login with FTP, the first directory you see is your home directory.
The path to your home directory is in the format:
/home/username/X/htdocs/
Where username is your hosting account username (see the top of your welcome letter), and where X is a unique alphanumeric string. You can determine this string by examining the site configuration in the control panel. You can also determine this string by executing an "info" script (see the scripting page for a sample).
The home directory is commonly used by scripts, which need to know the "full path to the script". For example,
/home/blazingfibre/ABCD1234/cgi-bin/script.cgi
Your "webroot" or "document root" directory is:
/home/username/X/htdocs/
Note: on multisite accounts, the webroot is changed to the directory you specified when you added the site.