Create Dynamic Stamp with Checkbox

I am completely new to dynamic stamps and have zero knowledge of javascript, but have managed to cobble together various javascript from google to create a Stamp with the date automatically populating : 

event.value = (new Date()).toString(); AFDate_FormatEx("h:MM tt dd/mm/yyyy");

And 2 empty fields that the user can input text (name and code): 

if (event.source.forReal && (event.source.stampName == "#hA4B5jvsuNXthXqaB8murC")) {
if ("ok" == app.execDialog(dialog1)) {
this.getField("Field1").value = dialog1.field1;
this.getField("Field2").value = dialog1.field2;
}
}

I would like to add 2 checkboxes to the stamp (Invoice and Credit Card) but I have no idea what javascript I need, or where to put the javascript to get the boxes to work.

Any help or advice would be very much appreciated.

Thanks