Create Users on Your Mac Running Mountain Lion
Before users can share folders and drives (or have their own accounts on your computer, for that matter), they must have an account on your Mac. In OS X Mountain Lion, you can create two different kinds of accounts for them — a User Account or a Sharing Account.
When you create a User Account for a person (User 1), the account has its own Home folder (called — what else? — User 1), which is filled with User 1’s files. Nobody but User 1 can access files in this Home folder unless, of course, User 1 has provided someone the account name and password.
When you create a Sharing Account for a person (Sharing 1), the person using that account doesn’t have a Home folder and can’t access other users’ Home folders. Sharing 1 can access only the Public folders inside all the Home folders on that Mac.
You can create a new User Account only in the Users & Groups System Preferences pane. You can create a new Sharing Account in either the Users & Groups or Sharing System Preferences panes.
When you click the + button under the Users list in the Sharing System Preferences pane and choose a contact in your Contacts (as opposed to choosing an existing user account), you create a Sharing Account for that person.
Anyone can remotely access files or folders in your Public folder(s) over a LAN (local area network) or the Internet. But if you want them to be able to access folders or files other than those in the Public folder(s) on your Mac, they need either a User Account or a Sharing Account.