Just install this extension the usual way like any other TYPO3 extension.
Get the extension
In the TYPO3 backend you can use the extension manager (EM).
- Switch to the module “Extension Manager”.
- Get the extension
- Get it from the Extension Manager: Press the “Retrieve/Update” button and search for the extension key ns_sharethis and import the extension from the repository.
- Get it from typo3.org: You can always get the current version from https://extensions.typo3.org/extension/ns_sharethis/ by downloading either the t3x or zip version. Upload the file afterwards in the Extension Manager.
Activate the TypoScript
The extension ships some static TypoScript code which needs to be included.
- Switch to the root page of your site.
- Switch to the Template module and select Info/Modify.
- Click the link Edit the whole template record and switch to the tab Includes.
- Select [NITSAN] ns_sharethis at the field Include static (from extensions):
- Include [NITSAN] ns_sharethis at the last place.