You need to integrate your form and php form processor with Wordpress. One method to do this in your theme as follows.
Create a page template in your theme folder, as described here. And put your form markup in it.
Don't specify an action on your form, and add a hidden field to your form with arbitrary name and value. We will check against, and then look for that input to handle your form input, For example:
<?php /* Template Name: My Form */ ?> <form method="POST"> <input type="hidden" name="my_hidden_field" value="xyz"> .... </form>
Now create a page in WP Admin and assign above created template. Load this page in browser to display your form.
Next put this code in functions.php of your theme
add_action( 'init', function() { if ( empty( $_POST['my_hidden_field'] ) ) { return; } // handle form submission include "xxx_insert.php"; // Replace xxx_insert.php with exact path to php file }
Other methods to achieve the result is writing a plugin or shortcode.
I hope this may helps!
/wp-content/themes/mytheme/xxx_insert.php