Groups can refer to either a logical or physical collection of PBX Clients. There is no limit to the number of groups you can have.
Clicking on M3 Setup > Groups should display a screen like this.
Each PBX Server that you add to M3 belongs to a single Group and the following settings will be applied to all the Servers of the Group
Firewall rules,
Services that should be set to always start on boot
SSH Keys that belong to the group
Before changing firewall settings, it's recommended you read the Firewall documentation
On the left side of your screen you will see a list of all your Groups and a button to create "New Group"
Pressing the new Group button will prompt you to give your new Group a name
You can now manage your Group Settings and then go into your servers and assign any server to your new Group
