create a node outside of drupal
Unless you known exactly what you are doing, don't try to integrate with Drupal at the database level.

Drupal database schema is dynamic. Tables to store nodes information are added and modified when you add fields or change theirs settings. So your database query will need to be checked for every changes. This could easily become a maintenance nightmare.

Any module can, an many do, add custom behaviors on node insertions and updates through Drupal hooks system. Inserting content in the database without using Drupal's API would bypass these added behavior and potentially create inconsistent data.

If you must really do it outside Drupal, you can either bootstrap Drupal in your PHP standalone script to be able to use its API or use the Services module to provides a REST API for node CRUD operations.

To bootstrap Drupal in your PHP script, use the following code. Note that most of Drupal's code expect the current dir to be Drupal's one. Drupal also register its own session handler that may conflicts with yours.

chdir("/path/to/drupal");
require_once './includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);