AddThis is a content-sharing platform that provides tools that make it easier to share content across the social web.
To add AddThis:
First, go to AddThis and create an account.
You need to receive an integration code for your website.
Go to your SITE123 website.
In the Website Editor, click Settings and select Plugins from the drop-down list.
Click the Manage button.
Click the Add New button and select Add New Plugin.
Type AddThis in the search bar and click Add.
In the Application ID field, enter the relevant snippet from the code you got from AddThis - this is your unique verification code.
Insert the code, Enable it, and click Save.
Publish your website to update it with the changes you've made.