Checkbox submit PHP

I want to select a couple of rows with my "Checkbox Input" to see what customer i selected and with those selected customers i want to check the database for their payment information, so i can create an xml of it. (for the bank)

Im not very famaliar with arrays because this must be done with an array i guess.

I cant find the solution is needed my code

<div class="uk-width-1-1">
  <?php $users = $db->select(" SELECT as_bestanden.factuurnummer,as_bestanden.categorie,as_bestanden.datum,as_bestanden.id,as_bestanden.user_id, as_user_details.user_id, as_user_details.first_name,as_user_details.last_name FROM as_bestanden INNER JOIN as_user_details ON as_bestanden.user_id=as_user_details.user_id WHERE as_bestanden.categorie = 'fda' ORDER BY as_bestanden.datum DESC ");?>
     <table id="dt_default" class="uk-table" cellspacing="0" width="100%">
                        <thead>
                        <tr>
                            <th></th>
                            <th>Factuurnummer</th>
                            <th>Lidnaam</th>
                            <th>Datum factuur</th>
                            <th>Categorie</th>
                            <th>Acties</th>
                        </tr>
                        </thead>
                        <tbody>
                        <?php foreach ($users as $user): ?>
                        <tr>
                            <td>
                                <p>
                                    <input type="checkbox" name="checkbox_factuur" id="checkbox_factuur" data-md-icheck />
                                </p>
                            </td>
                            <td>
                                <?php echo e($user['factuurnummer']); ?>
                            </td>
                            <td>
                                <?php echo e($user['first_name']); ?> <?php echo e($user['last_name']); ?>
                            </td>
                            <td>
                                <?php $date = date_create($user['datum']);
                                echo date_format($date, 'd-m-Y'); ?>
                            </td>
   <td>
     <?php $categorie = e($user['first_name']); ?>
     <?php if ($categorie='fda') { ?>Factuur door afnemer <? } ?>
   </td>
                            <td>
                                <a class="md-btn" href="/dashboard/admin/facturen/bestanden/<?php echo e($user['factuurnummer']); ?>.pdf" download>Download Factuur</a>
    </td>
  </tr>
<?php endforeach; ?>
</tbody>

Thanks, if you need more information just tell me