facebook button

where must i place this code to use the facebook like button.

i have tried is with the function.php but a get an error:

<div id="fb-root"></div>
<script>(function(d, s, id) {
  var js, fjs = d.getElementsByTagName(s)[0];
  if (d.getElementById(id)) return;
  js = d.createElement(s); js.id = id;
  js.src = 'https://connect.facebook.net/de_DE/sdk.js#xfbml=1&version=v2.11&appId=251192335408952';
  fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>

this is the code for the button inside a page:

<div class="fb-like" data-href="https://developers.facebook.com/docs/plugins/" data-layout="standard" data-action="like" data-size="large" data-show-faces="true" data-share="true"></div>