Inserting checkbox values into multiple rows

I have an echo of a number of groups a user is a member of.

It will output multiple checkboxes. The value of the checkboxes (groupid)+ 2 hidden values need to be inserted into a row in a new table.

How do I insert the values per checkbox into separate rows?

<?php

$user=$_SESSION['SESS_USERID'];
if(isset($_REQUEST['user'])){
$user = preg_replace('#[^a-z0-9]#i', '', $_GET['user']);
}

if(isset($_REQUEST['id'])){
$id = preg_replace('#[^a-z0-9]#i', '', $_GET['id']);
}

$sql="SELECT * FROM groepsleden,groepen,werken WHERE groepsleden.groepid=groepen.groepid
AND groepsleden.userid='$user'AND werken.werkid='$id' ORDER BY groeplidid DESC ";

$result = $conn->query($sql) or die ("The query could not be completed. try again");

if ($result->num_rows > 0) {
      echo" <table>";

while ($row = $result->fetch_assoc()) {
      echo"<tr>
      <td bgcolor='#1E1E1E'>&nbsp;</td>
      <td bgcolor='#1E1E1E'><div align='right'>
      <input name='groepid' type='checkbox' value=" . $row['groepid'] . ">
      <input type='hidden' name='werkid' value=" . $row['werkid'] . ">
      <input type='hidden' name='userid' value=" . $row['userid'] . ">
      </div></td>
      <td bgcolor='#1E1E1E'>Paats dit werk in &nbsp;<a href='groep.php?
      id=" . $row['groepid'] . "'</a>".$row["groepsnaam"]."</span></td></tr></table>
}
} 
?>

<?php
$sql=$dbo->prepare("INSERT INTO groepwerken(werkid,groepid,userid)
VALUES ('$werkid','$groepid','$user')");
$sql->bindParam(':werkid',$werkid,PDO::PARAM_INT);
$sql->bindParam(':groepid',$groepid,PDO::PARAM_INT);
$sql->bindParam(':userid',$userid,PDO::PARAM_INT);