how to add multiple selection for a checklist

Describing what I am trying to do:

1.- Adding an input type="checkbox" that allows more than one selection.

2.- Modify the contact form email that I receive with the visitor's information.

You can see my website contact form at:
empleos.php

or you can download the files from:

<removed>

Explaining what I have tried and where I am getting stuck:

I have an input type="checkbox" which should allow the visitor to choose one or more options. It seems fine, but I tested it choosing two different options, when the contact form arrives to my email, only one option is included.

Phone number: +51.1.654.9249
Skype: roxana.castaneda

Please help urgently!
Thanks.

In PHP, to have a checkbox group pass multiple values, the names of the checkboxes need to end with "[]" to create an array:

<label>

      <input type="checkbox" name="Color[]" value="Red" id="Color_0" />

      Red</label>

    <br />

    <label>

      <input type="checkbox" name="Color[]" value="Green" id="Color_1" />

      Green</label>

    <br />

    <label>

      <input type="checkbox" name="Color[]" value="Blue" id="Color_2" />

      Blue</label>

    <br />

    <label>

      <input type="checkbox" name="Color[]" value="Yellow" id="Color_3" />

      Yellow</label>

    <br />

next, in the WA_UniversalEmail/Templates/contactus.php file, find the following line:

<?php echo(str_replace("\n","<BR />",$pval)); ?>

and change it to:

<?php if(is_array($pval)) { ?>

<?php echo(str_replace("\n","<BR />",implode(", ",$pval))); ?>

<?php } else { ?>

<?php echo(str_replace("\n","<BR />",$pval)); ?>

<?php } ?>