Please follow this installation process: General installation process
The archive file content has to be uploaded to: app/code/Magetrend/NewsletterMaker/
The extension is not working without the license key. If you don't have it or don't know yours, please follow this article: http://www.magetrend.com/magento-2-newsletter-maker/user-guide/licensing.
To install the license key, please go to:
Stores >> Configuration >> Magetrend Extensions >>Newsletter Maker>> Information & License
Enter the license key, and press "Save Config" button.
Note: please use development license key for non-production setups