WordPress’s codex.wordpress.org
is big friend about anything related to the WordPress system . you can import WordPress system into your web app
by looking at the following link:
Integrate wordpress with your app
WordPress says :
In order to transform regular PHP pages into ones that utilize WordPress, you need to add either of the following code snippets to the start of each page.
<?php
define('WP_USE_THEMES', false);
require('./wp-blog-header.php');
require('/the/path/to/your/wp-blog-header.php');