From within your Firewall Overview, you will see a list of all your Servers and any Services (OpenStack or DRAC's etc). Locate the row for the Server or Service you want to Apply a Rule Group too and press the "Choose" button;

You will then see an option for a Drop Down list, this will contain all of the available Rule Groups for you to select from;

Select the Rule Group that you would like from the list and click the "Save" button;

That is it! The Rule Group is then applied to the server.

Alternatively, you can press "Cancel" at any time and the changes will be reverted.

Changes to the Firewall Rule Group are applied the next time the Firewall Reloads, this is typically once every 30 minutes.