The Create Clusters screen is where you set up Oracle Grid Infrastructure, which is the software that consists of Oracle Clusterware and Oracle Automatic Storage Management (Oracle ASM).
When you create clusters, you are essentially clustering all the virtual machines from both compute nodes together within a virtual machine group. For the most part, the screen for creating clusters is automatically populated based on the information you provided in the earlier screens. However, you must provide a SCAN name for the database cluster that you are setting up.
Oracle Database clients connect to the database using SCANs. The SCAN and its associated IP addresses provide a stable name for clients to use for connections, independent of the virtual machines that make up the cluster.
The SCAN is a virtual IP name that is associated with the entire cluster. The SCAN works by resolving multiple IP addresses in the cluster handling public client connections. When a client submits a request, the SCAN listener listening on a SCAN IP address and the SCAN port is made available to a client. Because all services on the cluster are registered with the SCAN listener, the SCAN listener replies with the address of the local listener on the least-loaded node where the service is currently being offered. Finally, the client establishes connection to the service through the listener on the node where service is offered. All of these actions take place transparently to the client, without any explicit configuration required in the client.