What Do I Insert Here?

I have been given a PHP snippet from my email marketing platform to install on my Wordpress site roadrunneremails.net. The purpose of it is to pass new email subscribers from my site to my 3rd party email marketing platform. The snippet goes a little like this…

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<?php $url = "INSERTURLHERE"; $data = array( "method" => "listSubscribe", "params" => [ "api_key" => "INSERTAPIKEYHERE", "list_id" => "INSERTLISTIDHERE", "emails" => [ "BUT WHAT DO I INSERT HERE?" ] ] ); $options = [ 'http' => [ 'method' => 'POST', 'content' => http_build_query(array('data' => json_encode($data))) ] ]; $context = stream_context_create($options); $result = file_get_contents($url, false, $context); *end snippet* I understand what to put in the $url section, the api_key section and the list_id section but I have no idea what to put in the "BUT WHAT DO I INSERT HERE?" email section to pass form input from my Wordpress site. Does anyone have any suggestions? Please bare in mind that my PHP knowledge is shoddy at best. Looking forward to any advice I can get,