Accessing multiple nested Arrays and PHPmailer variables

So I'm creating a file where users can add their content information for a frontend template. Whatever they type in this php file will show on the site. Sort of have two issues:

1. I need to be able to create a nested array and be able to call all or just one of the nested array elements.
2. How do I call a variable from the setup function to PHPmailer: $mail->Username and $mail->Password

Here is what I have that works so far:

function setup() {
    return array(
        'firstname' => "Your first name",
        'lastname' => "Your last name"
    );
}

extract (setup ());

Then I can call any element from the array into the HTML

<?php echo $firstname; ?>

Here's what I'd like to do:

function setup() {
    return array(
        'firstname' => "Your first name",
        'lastname' => "Your last name",
        /**
         * Would like a nested array but need to be able to call "nested" or any value within individually, anywhere in my html.
         */
        $nested = array(
            $set1 = array(
                "value1",
                "value2",
                "value3",
            ),
            $set2 = array(
                "value4",
                "value5",
                "value6",
            )
        ),
        /** 
         * I need the 'mail' and 'mailpass' to link to $mail->Username and $mail->Password
         * */ 
        'mail' => "[email protected]",
        'mailpass' => "password"
    );
}

extract (setup ());

Then call it, something like this:

<div>
  <h1><?php echo $nested[0][1]; ?></h1>
  <ul>
    <li><?php echo $nested[1][2]; ?></li>
    <li><?php echo $nested[1][2]; ?></li>
  </ul>
  <div>
    <?php echo $nested[$set1]; ?>
  </div>
  <div>
    <?php echo $nested[$set2]; ?>
  </div>
</div>

And have PHPmailer do this:

if ( array_key_exists( 'email', $_POST ) ) {
    //From this
    ..
    $mail->Username = '[email protected]';
    // SMTP password
    $mail->Password = 'password';
    ..
    //To Something like this
    ..
    $mail->Username = $mail; // This is the variable from the setup function
    // SMTP password
    $mail->Password = $mailpass; // This is the variable from the setup function
    ..
}

Are loops required for these 2 issues? If so, how would I go about this? Thanks in advance

UPDATE #1 / PARTIAL SOLUTION

Turns out, I DO need a loop. Took me a while to figure out but I needed multiple values, that would generate multiple list items.

In this case an associative array and a foreach key loop is needed. Let's create a new function:

function associativeArray() {

    // Create the associative array
    $associativeArray = array(
        'Key name a' => array(
            'job' => 'Front End Dev',
            'name' => 'Dave'
        ),
        'Key name b' => array(
            'job' => 'Back End Dev',
            'name' => 'Paul'
        ),
        'Key name c' => array(
            'job' => 'Full Stack Dev',
            'name' => 'James'
        ),
        'Key name d' => array(
            'job' => 'Stackoverflow Dev',
            'name' => '( ͡° ͜ʖ ͡°)'
        ),
    );

    // loop the associative array to display key & values
    foreach($associativeArray as $key => $array) {
        /**
         * Call the $key value(in this case it's a title), next..
         * we'll access the $key's index elements with $array['indexname']
         */
    echo
        '<li>
            <h3>'.$key.'</h3>
            <h6>'.$array['job'].'</h6>
            <p>'.$array['name'].'</p>
        </li>
        ';
    }
}

Next, call the function where ever needed. This is going in an unordered list:

<ul><?php echo associativeArray(); ?></ul>

Finally, the output:

<ul>
  <li>
    <h3>Key name a</h3>
    <h6>Front End Dev</h6>
    <p>Dave</p>
  </li>
  <li>
    <h3>Key name b</h3>
    <h6>Back End Dev</h6>
    <p>Paul</p>
  </li>
  <li>
    <h3>Key name c</h3>
    <h6>Full Stack Dev</h6>
    <p>James</p>
  </li>
  <li>
    <h3>Key name d</h3>
    <h6>Stackoverflow Dev</h6>
    <p>( ͡° ͜ʖ ͡°)</p>
  </li>
</ul>