is it safe? insert the data to db by user ..?
if(!empty($_POST['user_name']) || !empty($_POST['email'])){
$user_login  = $_POST['user_name'];
$user_email  = $_POST['email'];
$random_password = wp_generate_password(5 , true );
wp_create_user( $user_login, $random_password, $user_email )

} else {
echo 'The user name or E-mail is empty';

}

<?php if ( is_email( 'email@domain.com' ) ) {
      echo 'email address is valid.';
} ?>

<?php
       $username = $_POST['username'];
       if ( username_exists( $username ) )
           echo "Username In Use!";
       else
           echo "Username Not In Use!";
?>