Where possible you should think about tooltips--those small popup frames that appear while you hover the mouse over some item and contain useful information about the item. Tooltips provide the basic reminders that help the user ignore the application's written documentation. Tooltips should be just a little verbose, perhaps taking up 3 or 4 lines of text. Aim to inform with the minimum number of words.
You add tooltips to widgets by first selecting the widget. Select the text area of your fileentry1 widget--this will select something called combo-entry1 which is contained within the Gnome File Entry widget. Then in the Properties window click on the Basic tab. On that page you will see the Tooltip text entry about halfway down. Simply type in the required text, such as:
Name of the file whose contents is to be counted.
Now hover the mouse over the file entry field on your canvas and the tooltip should pop up.
An interesting question is whether the tooltip should be associated with the file entry field as we have done or with the label of the field, or both? The answer is left as an exercise for the reader! We prefer to associate the tooltip with just the entry field itself since that is where the mouse will be hovering while you are thinking about it. On the other-hand Glade's own interface associates the tooltips with the labels.