Your ConfigurationData is essentially a list of nodes that you want a Configuration to apply to.

From Part 1:

ConfigurationData – This is, basically, a list of the nodes that PowerShell DSC will configure as per the Configuration.

Example:

@{
	AllNodes = @(
		@{
			NodeName	= "*"
			LogPath		= "C:\Logs"
		},

		@{
			NodeName		= "Win2016DC01"
			Role			= "PDC","DC","XPS"
		}
	)
}

Let us unpack this:

@{
	AllNodes = @(
		@{

Here we create a hashtable which does not have to be named, and then we create the AllNodes hashtable. AllNodes must be named thusly, this is so PowerShell DSC knows what you’re throwing at it.

		@{
			NodeName	= "*"
			LogPath		= "C:\Logs"
		},

Here we use a wild card to indicate that we want all nodes to have a LogPath of C:\Logs

		@{
			NodeName		= "Win2016DC01"
			Role			= "PDC","DC","XPS"
		}

This is where it gets interesting.
Here we can see that I specify a node by name, Win2016DC01, and I specify which roles it should have. As you can see, I can specify multiple roles on one line, separated by a comma.
This will then tell a Configuration which Features/Roles/Settings a node should have, and then create MOF files appropriately. This configuration is naturally very basic.

Unfortunately the Configuration I showed you in Part 1 would not be able to make use of a ConfigurationData file like the one I showed you here, so here is an appropriate Configuration:

Configuration MyDscConfiguration
{
	Node $AllNodes.Where{$_.Role -eq "XPS"}.NodeName
	{
		WindowsFeature XPS-Viewer
		{
			Ensure = "Absent"
			Name = "XPS-Viewer"
		}
	}
}

As you probably noticed, here we don’t specify a node by name, but instead specify that all Nodes in the ConfigurationData with a role of XPS will have the WindowsFeature XPS-Viewer removed.

This brings Part 3 to an end. I hope it has been helpful and informative.