G Merge Plus: Document Merge and Mail Merge has two parts.
The main functionality for doing document merges and mail merges is with a Google Sheets add-on, which you can find in the G Suite Marketplace.
Enhanced functionality such as creating and sharing templates, managing your subscription, and adding users to your team (for paid Team accounts) is in our standalone application, which you can access by launching it from the Google apps launcher or visiting https://app.gmergeplus.com
Meanwhile, to start using the add-on, you'll need to go to Google Sheets, click Add-Ons, navigate to G Merge Plus, and click Start.
To perform document and mail merges, you can follow our step-by-step guide to set up the add-on to work for your specific use cases.