The latest version [from version 3.90 only] of CORE plugin supported following new features:
* Manage Inline Scripts
* Manage Inline Styles
With the new above features, it's quite easy to integrate with other tools, like Olark
Step by step to got it work on your nopCommerce website:
* Register an account in Olark website
* Go to https://www.olark.com/settings/code to get your embedded script code
* Click on "Manage Inline Scripts" menu item (from Plugin Settings dropdown button) in CORE plugin's setting page
* Click on "Add new" button
* Name your inline script, ex.: Olark
* Paste the embedded code to "Scripts" field
* Specify an widget zone to render that embedded code, in this case, it should be "body_end_html_tag_before"
* Save it, and go to your publish store to see the result.
Hope that help :)