When you order servers on g-portal you are purchasing slots basically, starting at a minimum of 10 per server. If you want to setup a cluster you need to purchase at least 20 slots, then create a server and configure it for one map. Then you repeat using your other 10 slots to setup another sever for another map. All you really need to do is insure that the Cluster ID for bother servers are unique and match. That can be setup in the Basic Settings section of your dashboard.