Its important to have user accounts so you can save data and maybe log in and out of a device/cmp to another one. The purpose of the user account is to help save your stuff and personalize your device. The features are more data storage to add up, and ability to make more accounts for others so each of you can personally have their own account and save their own data on their own. Administrator accounts are the highest and have the most power of all, they are in charge of everything, especially giving permission to apps you may have downloaded and removing system apps. Users rights are the tasks specific users can do to make sure no user has too much power or less so to speak and it means what you are able/not able to do as well.
Hard disks, CDs, and flash drives are all storage mediums.
