Default directory structure of website

Is there an article/tutorial that explains the default directory structure of a website. I'm unclear as to how the root/home directory relates to the 'public_html' and 'public_ftp' directories.

As one example, I've created an 'images' folder under the root/home directory. In my 'default.htm' file, I'm trying to add an image tag, which references one of the images in my 'images' directory, to display, but the image never shows up (only the broken/missing image icon).

I've not seen a directory structure like this one before, and I've used several other hosting companies in the past. I'd like to have a better understanding of the directory structure.

Thanks!