This folder and the folder named after your PC are created by Roon Server when you drag and drop ripped albums from your PC into Roon’s user interface window.
You don’t need to add further files and folders using File Explorer there. Just put them in the top-level InternalStorage folder as others have suggested.
If you want to declutter the top-level folder, then you can always create folders corresponding to artists and put their ripped albums in the relevant artist folder…