Using the generic type 'System.Action'requirs 1 type arguments

First off, there is a lot of info out there: a simple google could have got you relevenat info very quickly: MSDN[^]

You use an Action<T> delegate to pass a method as a parameter to another method without having to declare a formal delegate. The method you pass can return no value, and takes a single parameter of type "T".

This is taken direct from MSDN:

delegate void DisplayMessage(string message);
   public static void Main()
   {
      DisplayMessage messageTarget; 
      if (Environment.GetCommandLineArgs().Length > 1)
         messageTarget = ShowWindowsMessage;
      else
         messageTarget = Console.WriteLine;
      messageTarget("Hello, World!");   
   }      
   private static void ShowWindowsMessage(string message)
   {
      MessageBox.Show(message);      
   }

Can be simplified to:

   public static void Main()
   {
      Action<string> messageTarget; 
      if (Environment.GetCommandLineArgs().Length > 1)
         messageTarget = ShowWindowsMessage;
      else
         messageTarget = Console.WriteLine;
      messageTarget("Hello, World!");   
   }      
   private static void ShowWindowsMessage(string message)
   {
      MessageBox.Show(message);      
   }
</string>

Both examples do the same job: you can specify that output goes to a message box (via ShowWindowsMessage) or to the console once in advance, and never have to check again.
The second example just saves you having to declare a delegate to define what method signatures can be used.