A control descriptions field can be blank, show a symbol, or show text. 

To show text in a field:

1. Open a window to edit the control in question. 
2. Select the relevant control descriptions field by clicking in the field. 
3. Use the button "Text" (3x5) in the toolbar below the symbol palette to change the field from a symbol field to a text field.
4. A text field appears instead of the palette.
5. Enter the text.

Hint: Use the "Two Symbols" toolbar button to split the field to show two texts.  Use the "Diagonal line" toolbar button to show a diagonal line across the field.