Multisite structure

I already have Grav working well for my site at example,com. Now I want to add a subsite that will use a different theme. I do not understand this part of the instructions:

If you choose sub-directories or path based URLs for subsites, then the only thing you need is to create a directory for each subsite in the user/sites directory containing at least the required folders config, pages, plugins and themes.

Does this mean that I create a single new sub-directory in /user with the name of the subset? Or do I create two new sub-directories, one with a copy of everything from the old /user but with the main domain name and one new sub-directory with the new subset name?

I also would like to have this explained in depth.
As I use the admin tool the directory was not automatically updated and I really don't know how the structure has to look.

There are a lot of folders now in the 'user' folder and I don't know which ones I have to copy to the 'user/sites'.

I also am not sure how this works in admin.

Let's say I created in the admin tool 3 folders 'DE', 'FR' and 'IT'.
Is the path for this 'user/sites/de' (for folder 1) or is it 'user/de'?