When you first open your "Files" application you will see two folders: a "Private" folder and a "Public" folder. By default, the "private" folder will be visible only to you and the "public" folder will be visible to anyone, whether or not they have a Keep&Share account. This also means that all files in the "public" folder will be visible to anyone and any files in the "private" folder will be visible to you. See the image below:
You can rename the folders and change the sharing for them at any time. These are only the starter folders in your account to make sharing easy if you want to keep your files public or private.