Me podrian explicar este codigo php porfavor

[mrabros]

<?php
session_start();
include "conecta.php";
$result = mysql_query("select * from productos");
$row = mysql_fetch_array($result);
$dato=$_REQUEST['opc'];
$result2 = mysql_query('SELECT * FROM productos WHERE cod_producto=\''.$dato.'\'');
$prueba=mysql_affected_rows();
$result3 = mysql_query('select * from usuarios WHERE nusuario=\''.$_SESSION['k_username'].'\'');
$reg1 = mysql_fetch_array($result3);

$result4 = mysql_query('select cod_client from usuarios WHERE nusuario=\''.$_SESSION['k_username'].'\'');
$reg2 = mysql_fetch_array($result4);

$result5 = mysql_query('select email from usuarios WHERE nusuario=\''.$_SESSION['k_username'].'\'');
$reg3 = mysql_fetch_array($result5);

$result6 = mysql_query('select direccion from usuarios WHERE nusuario=\''.$_SESSION['k_username'].'\'');
$reg4 = mysql_fetch_array($result6);
$result7 = mysql_query('select nombre,apellido1,apellido2 from usuarios WHERE nusuario=\''.$_SESSION['k_username'].'\'');
$reg5 = mysql_fetch_array($result6);
?>


el for este no lo entiendo.....porfavor que alguien me lo explique

for($a1=0;$a1<$prueba;$a1++){
?>
<tr>
<input type="hidden" name="codclient" value="<?php print (mysql_result($result4,$a1, "cod_client")); ?>">
<input type="hidden" name="email" value="<?php print (mysql_result($result5,$a1, "email")); ?>">
<input type="hidden" name="direccion" value="<?php print (mysql_result($result6,$a1, "direccion")); ?>">
<input type="hidden" name="nombre" value="<?php print (mysql_result($result7,$a1, "nombre")); ?>">
<input type="hidden" name="ape1" value="<?php print (mysql_result($result7,$a1, "apellido1")); ?>">
<input type="hidden" name="ape2" value="<?php print (mysql_result($result7,$a1, "apellido2")); ?>">
<input type="hidden" name="cod" value="<?php print (mysql_result($result2,$a1, "cod_producto")); ?>">
<input type="hidden" name="nombre" value="<?php print (mysql_result($result2,$a1, "nombre")); ?>">
<input type="hidden" name="precio" value="<?php print (mysql_result($result2,$a1, "precio")); ?>">
<input type="hidden" name="stock" value="<?php print (mysql_result($result2,$a1, "Stock")); ?>">
<td><input type="text" name="cod1" value="<?php print (mysql_result($result2,$a1, "cod_producto")); ?>" maxlength="4" size="4" disabled></td>
<td><input type="text" name="producto1" value="<?php print (mysql_result($result2,$a1, "nombre")); ?>" maxlength="100" size="50" disabled></td>
<td><input type="text" name="precio1" value="<?php print (mysql_result($result2,$a1, "precio")); ?>" maxlength="7" size="7" disabled></td>
<td><input type="text" name="stock1" value="<?php print (mysql_result($result2,$a1, "Stock"));?>"maxlength="2" size="2" disabled></td>
<td><input type="text" name="unidades" value="" size="3" maxlength="3"></td>
</tr>
</table>

</div>


<?php
}
?>
Porfavor neccesito buestra ayuda ... gracias