Step 1. Download the Magento extension module from Github: https://github.com/sendsmaily/smaily-magento-extension
Step 2. Install Smaily module like this: http://devdocs.magento.com/guides/v2.0/cloud/howtos/install-components.html
Step 3. Setup
To change Smaily configuration, log into your Magento admin.
Go on the Main Menu to "Stores" (1) -> "Configuration" (2).
On Configuration page, open tab "Smaily email marketing and automation", then click on "Plugin Configuration".
On Smaily Magento Plugin Configuration page, update your Smaily API details. Subdomain (1) is the subdomain of your Smaily account, for example if the account address is demo.sendsmaily.net, then enter the subdomain "demo", if your account address is asdfasd.sendsmaily.net, then enter "asdfasd", etc.
Enter the API username (2) and password (3). If you don't have API username and password yet, read from here how you can create them.