Enter a search term. In this case I am looking for files related to World War II. You could also do a search for something like "Maine Seafood." You have to enter a search term and do the search before you will see the screen pictured below.
Alternatively, you can search by file type by entering filetype: KMZ after your search term.
To clarify, you will have to open the file in Google Earth to see its contents. This method is just for finding files to use in Google Earth.