Step 1
Install modman - https://github.com/colinmollenhour/modman
Step 2
Run the following modman command:
$ modman clone https://github.com/Metrilo/metrilo-magento1-integration -b 'APIv2'
Step 3
Configure the plugin by going to "System" -> "Configuration" -> "Metrilo Analytics"
You can take the credentials from the Settings/Installation page of your Metrilo project.
Step 4
Flush your magento cache.
Step 5
The last step importing your historical orders by choosing the store on the "Current Configuration Scope", while still on the Configuration page -> Metrilo Analytics, and hit the Import button (if you use a Magento MultiStore installation, you will need to make the import for each store separately).