Php if for beginner

Unfortunately, you don’'t say what exactly is going wrong, but this should give you what you want:

<?php if ($page->intendedTemplate() ==  'article') :?>
   <meta name="keywords" content="<?php e($page->keywords()->isNotEmpty(), $page->keywords()->html(), $page->tags()->html()) ?>" />
<?php else: ?>
  <meta name="keywords" content="<?php e($page->keywords()->isNotEmpty(), $page->keywords()->html(), $site->keywords()->html()) ?>" />
<?php endif ?>

I don’t know if your articles are called article.txt or something else, since your $article in the code above is not defined, so you need to adapt this if necessary.