Is root folder or public_html, Is same?

Dear Sir,

I installed the wordpress in The root folder,and went to set up multi domains plugin.

But in the wordpress Manuals said, install to a WordPress Multisite which allows you to create a network of sites you need to: upload your new wp-config.php file into your public_html folder. and Create your blogs.dir directory public_html/wp-content/blogs.dir

I tried create public_html in root, but can not set up multy sites, then I upload the public-html to root folder wp-content,the sites have error too.

I should create /wp-content/blogs.dir and /wp-content/mu-plugins in the root folder and don't need create public_html
or I should create public_htmlwp-content/mu-plugins.