in the following example, i will assign some variables that belong to a class. But are assigned inside one of the function/methods. If you only assign it as $example and not as $this->example, it does not assign that variable to the entire class, only in that method/function.

class myClass
{
var $example;
var $example2;

function say_what()
{
    $example = 'Hi';
    $this->example2 = 'Hi again';

    echo '$example: '.$example."<br/>";
    echo '$example2: '.$example2."<br/>";
    echo '$this->example: '.$this->example."<br/>";
    echo '$this->example2: '.$this->example2."<br/>";
}
function say_again()
{
    echo '$example: '.$example."<br/>";
    echo '$example2: '.$example2."<br/>";
    echo '$this->example: '.$this->example."<br/>";
    echo '$this->example2: '.$this->example2."<br/>";
}

}

$convo = new myClass();
$convo->say_what();
$convo->say_again();

PRINT OUT

// this is $convo->say_what();
$example: Hi
$example2: //blank
$this->example: //blank
$this->example2: Hi again

// this is $convo->say_again();
$example: //blank
$example2: //blank
$this->example: //blank
$this->example2: Hi again // only this one assigned to class shows.