Administrators by default cannot access other user's folders. If you do not want other users on your system to access your folders, then you may have other folders that are not in your user folder. If these folders are NOT the System, Library, Applications, or Users folders, then you can simply drag any other folders to your Desktop, and other users will not be able to access them there. If you don't want to clutter up your desktop, then simply drag those folders to your UserName folder (that's your Home folder)