OS X El Capitan: Create a sharing-only user account
If you want to let someone use your computer, but you don’t want to create a user account for the person, you can create a sharing-only account to enable the person to access only the files and folders you specify.
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Choose Apple menu > System Preferences, then click Sharing.
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Select the File Sharing checkbox.
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Click the Add button
at the bottom of the Users list. -
Click Users & Groups, Network Users, or Network Groups, select a name, then click Select.
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Assign a password for the new sharing account, then click Create Account.
You can specify which folders a user can access and what level of access the user has. You can also specify which users can share your screen. For more information, see Share your files.