In the command string gadget, you can type in a command. It is advised that you specify the full path, or else AWeb might not be able to execute the command. You can click on the button to pop up a file requester, so you can easily pick the command.
In the arguments string you specify the arguments for the command. Any text you type here will be passed to the external program, but the first two or three %s instances will be replaced by parameters from AWeb. These parameters differ for each command, but you can click the gadget to pop up a short descriptive list.
Instead of a program, you can specify a DOS script. If you do, make sure that the script bit for this file is set. You can set this bit either by the DOS command
protect script_name +sor by the Workbench Information program (select the Script checkbox).
Note that an external program setting will only be recognized if both fields, command and arguments, are supplied.