<?php
$currenturl = 'http://' . $_SERVER['SERVER_NAME'] . $_SERVER['REQUEST_URI'];

// Look at URL
$pos1 = strpos($currenturl, "?value-one");
$pos2 = strpos($currenturl, "?value-two");
//...

// If URL has "?value-one" create new custom field and add value-one
if($pos1 == true) {
add_post_meta($id, 'my_new_custom_field_name', 'value-one', true);
}
// If URL has "?value-two" create new custom field and add value-two
 elseif($pos2 == true) {
add_post_meta($id, 'my_new_custom_field_name', 'value-two', true);
}
// ...
?>