how to install extension manually in 2.1.
The primary way to install an extension is through composer (http://devdocs.magento.com/guides/v2.2/comp-mgr/install-extensions.html).
If you have a zip file, you can install it by copying it into the app/code/ directory.
You can keep your code inside app/code folder in root of magento installation.
Just keep your code file at above location and run below command to work your extension,
If your magento instance would be 2.0.* or 2.1.* run below command,
php bin/magento setup:upgrade php bin/magento setup:static-content:deploy php bin/magento cache:flush
If your magento instance would be 2.2.* or greater version, Run below command,
php bin/magento setup:upgrade php bin/magento setup:static-content:deploy -f php bin/magento cache:flush
check now in your admin panel and frontend.