To enable the social media 'Share This' feature on your product page, you first need to set-up an account with Share This.
To do this, first go here and sign up for an account: https://sharethis.com
After you've signed up, log into your account and first select your domain.
Next, click on Apps Directory in the top left and then click on the 'Inline Share Button' and enable it so it's added to your list of Enabled Tools.
Finally, click on Settings in the left side menu and you'll then find your Property ID on the right. This is the ID you need to send to your Web Ninja contact.