Let's Encrypt is a certificate authority that provides free certificates for SSL encryption via an automated process designed to eliminate the current complex process of manual creation, validation, signing, installation, and renewal of certificates.
1.Go to Subscriptions -> the domain you want to install the SSL for.
2. Click on Let’s Encrypt (If you can’t see this option call support as we can install the extension for you)
3. Fill in the email address and select the include a www. Option, you can also select the webmail option if you’re hosting mail on your server. Click Install
4. You’ll be redirected back to the Domain and have this bar at the top
5. This will enable the site to use the SSL. You'll now need to configure your site to operate over SSL. This is usually done within the sites .htaccess or CMS.