In OOP:

private - you can access that property only from inside the class

class Private
{
	private $foo;
	
	function setFoo($foo)
	{
		$this->foo = $foo;
	}
	
	function getFoo()
	{
		return $this->$foo
	}
}

$privateObj = new Private;

$privateObj->foo = 'bar'; // Returns error
echo $privateObj->foo; // Returns error

$privateObj->setFoo('bar') // Sets the $foo parameter = 'bar';
echo $privateObj->getFoo() // Returns 'bar';

public - you can access that property from an object

class Public
{
	public $foo;
	
	function setFoo($foo)
	{
		$this->foo = $foo;
	}
	
	function getFoo()
	{
		return $this->$foo
	}
}


$publicObj = new Public;

$publicObj->foo = 'bar'; // Sets the $foo parameter = 'bar';
echo $publicObj->foo; // Returns 'bar';

$publicObj->setFoo('bar') // Sets the $foo parameter = 'bar';
echo $publicObj->getFoo() // Returns 'bar';

protected - you can access that property from inside the class and from inside of class's children

class Protected
{
	protected $foo;
		
	function setFoo($foo)
	{
		$this->foo = $foo;
	}
	
	function getFoo()
	{
		return $this->$foo
	}
}


class ProtectedChild extends Protected
{
	
}


$protectedChildObj = new ProtectedChild;

$protectedChildObj->foo = 'bar'; // Returns error
echo $protectedChildObj->foo; // Returns error;

$protectedChildObj->setFoo('bar') // Sets the $foo parameter = 'bar';
echo $protectedChildObj->getFoo() // Returns 'bar';

Hope this helps