How to add Facebook SHARE Button to a Website or Blog
Adding a FaceBook Share button requires for Blogs or Websites to make it easy for visitors to share the contents with their friends. In order to do that, Facebook provides a Share button plugin, which can be easily integrated to your website or blog page.

Here we'll explain the steps on how to add Facebook Share button to your web or blog page;

First you need to get the Facebook Share button code

Login to Facebook and then go to Facebook social plugins page. 
Link: https://developers.facebook.com/docs/plugins/share-button

You will see a form and need fill it with the required details, as below.
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URL to Share – Here you need to enter the web page or blog post URL that you want people to share. Do note, Facebook allows you to generate the code specific to particular URL only and if you want the share button for individual pages then you need to generate the code for each URL separately or you can later modify the web address in the web page code it self.

Layout – Here you can choose the layout. You can see the preview to understand each layout option.

Once you fill in the form, click on the "Get Code" button to generate the Facebook like button code to add to your website or blogs HTML code. Choose the tab "IFRAME" and copy the code Facebook provides.

Now to add this to your site, choose a page (or pages) where you'd like to add a Share button and then drag an Embed Code element to that page. Paste the Facebook code into that Embed Code element.
Once you click out of the Embedded code element your FB Share Button will appear and the same will be available to all of your visitors once you publish the page.

Incase, if that option doesn't work for your web page or blog, you can try the other option to include the JAVA Script. Go to "HTML5" tab, there will be two parts of the code, copy both the parts of the code and paste it in a Notepad or Notes.
Insert the first portion into your main HTML/CSS code, ideally somewhere inside <body> tag and then place second part of the code to embedded code element, where you want to show the share button in the webpage or blog.