Social Share Buttons are buttons, for various social media platforms such as Facebook, Instagram, and Twitter, that you add to your website in order for people to be able to share your page on their respective social media account.
Steps:
From your Shopify admin, go to Online Store -> Themes.
Find the theme that you want to edit, and then click Customize.
Click Theme settings -> General -> Social Share Buttons.
Signup for an AddThis account here.
Activate and customize the tools that you would like to use on your site.
Go to the Get the Code page in your AddThis dashboard and copy your unique snippet of JavaScript under the HTML tab.
Login to your Shopify account.
Paste the snippet of JavaScript at Custom Script fields. In front of the snippet, insert a DIV classed as "addthis_inline_share_toolbox", then click Save.
The final look of the pasted snippet should be similar to this:
If you’ve activated an inline tool, there is a second snippet of code that you will need to add to your site. Copy the inline snippet from the Get the Code page in your AddThis dashboard and paste it into your Shopify theme where you would like your inline tool to appear.