After installing the plugin activate it. Once the plugin is active visit the plugin settings page. On the plugin setting page you will see Text box with License Key written on it.
Enter the License key you received in mail in the License key text box. You need to click the Activate Plugin button to activate the plugin. You will be notified if the plugin was successfully activated.
After the plugin is activated successfully you can configure the plugin as per your website requirement. Note the plugin can not be configured if it is not activated.So the first step after plugin installation is Activation.
In case you face any issues while activating the plugin then you can contact me. Most of the times it should work fine if you are using correct License key.