When use public, private or protected PHP

You use:

• public scope to make that variable/function available from anywhere, other classes and instances of the object.
• private scope when you want your variable/function to be visible in its own class only.
• protected scope when you want to make your variable/function visible in all classes that extend current class including the parent class.

More: (For comprehensive information): http://php.net/manual/en/language.oop5.visibility.php