The file paths given below assume a default PC installation to C:\Program Files. When installing content for The Sims, file icons and listed file types should not be considered reliable, as many of the extensions The Sims uses for custom content are also used by other programs, and those extensions may be associated with those programs. It is best to set Windows so that file extensions are always shown. Sub-folders are not recognized, except in the Downloads folder used for objects.
There is no need to do anything to the content files other than place them in the correct folders. In The Sims, different types of custom content are placed in different folders, depending on their file type.