array question

I'm a newbie at php and I'm sure you will be able to tell by my question. I'm just doing a simple form but my head is hurting from trying to figure out the correct syntax. I'm posting the form to $PHP_SELF an example from my $form_block = <p><b>*</b>Your Name:<br /> <INPUT type=\"text\" name=\"sender_name\" value=\"$_POST[sender_name]\" size=30></p> <p><b>*</b>Your E-Mail Address:<br /> <INPUT type=\"text\" name=\"sender_email\" value=\"$_POST[sender_email]\" size=30></p> <p>Phone Number:<br /> <INPUT type=\"text\" name=\"phone\" value=\"$_POST[phone]\" size=30></p> which finally leads to my question how do I do the $_POST[var] when it's an array(checkbox or radio button)? ex: <input type=\"checkbox\" name=\"product[]\" value=\"red\">red<br /> Am I making sense? If not please let me know :-) and I will try to remedy it. Michelle