Facebook Sdk Code 

<script>
  window.fbAsyncInit = function() {
    FB.init({
      appId      : '391270537927186',
      xfbml      : true,
      version    : 'v2.7'
    });
  };

  (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 = "//connect.facebook.net/en_US/sdk.js";
     fjs.parentNode.insertBefore(js, fjs);
   }(document, 'script', 'facebook-jssdk'));
</script>












just copy and paste the line of code below anywhere inside the <body> of your page:






<div
  class="fb-like"
  data-share="true"
  data-width="450"
  data-show-faces="true">
</div>




Source:http://www.discussdesk.com/facebook-login-using-php-web-sdk.htm
Source: https://developers.facebook.com/docs/facebook-login/web/