Explanation

Box 1: $cluster = Get-Cluster
The Get-Cluster cmdlet gets information about one or more failover clusters in a given domain.
This cmdlet can obtain a variety of configuration and state information about a failover cluster, including the following items, such as the EnabledSharedVolumes property.
Box 2: $cluster.EnabledSharedVolumes ="Enabled"
Box 3: Add-ClusterSharedVolume "Disk1"
The Add-ClusterSharedVolume cmdlet makes a volume available in the Cluster Shared Volumes in a failover cluster. The Cluster Shared Volume must be chosen from the disks in Available Storage (that is, disks that have been added to the cluster but not assigned to a specific use in the cluster).
References:
https://docs.microsoft.com/en-us/powershell/module/failoverclusters/get-cluster
https://docs.microsoft.com/en-us/powershell/module/failoverclusters/add-clustersharedvolume?view=winserver2