The Command Definition dialog is used to create commands. It can be invoked from the Control Definition dialog and the Screen Definition dialog.
Class is the command class. Choose one from those available.
Command is the command itself. Once you have selected a class the list of command for that class is available in the dropdown. Some classes do not have a command.
There are three edit boxes for command options. The labeling of these edit boxes changes to reflect the interpretation of the options for the different commands. There is also line at the bottom of the screen describing what the command does.
Var when clicked on brings up the Variable Selection dialog and places your choice from it in the first editing box.