WordPress at a glance
function is not described

wp_new_blog_notification() WP 2.1.0

Notifies the site admin that the setup is complete.

Sends an email with wp_mail to the new administrator that the site setup is complete, and provides them with a record of their login credentials.

No Hooks.

Return

Nothing (null).

Usage

wp_new_blog_notification( $blog_title, $blog_url, $user_id, $password );
$blog_title(string) (required)
Site title.
$blog_url(string) (required)
Site url.
$user_id(int) (required)
User ID.
$password(string) (required)
User's Password.

Code of wp new blog notification: wp-admin/includes/upgrade.php VER 5.0.3

<?php
function wp_new_blog_notification($blog_title, $blog_url, $user_id, $password) {
	$user = new WP_User( $user_id );
	$email = $user->user_email;
	$name = $user->user_login;
	$login_url = wp_login_url();
	/* translators: New site notification email. 1: New site URL, 2: User login, 3: User password or password reset link, 4: Login URL */
	$message = sprintf( __( "Your new WordPress site has been successfully set up at:

%1\$s

You can log in to the administrator account with the following information:

Username: %2\$s
Password: %3\$s
Log in here: %4\$s

We hope you enjoy your new site. Thanks!

--The WordPress Team
https://wordpress.org/
"), $blog_url, $name, $password, $login_url );

	@wp_mail($email, __('New WordPress Site'), $message);
}