Any value or formula you have previously entered for the current field is displayed in the formula bar. You can click in the formula bar to start editing, whereupon the focus moves from the grid to the formula bar, and the
and 
buttons alongside are enabled. This state is known as Edit Mode. The formula bar can only be active in one dialog at a time. Precisely how you use the formula bar to set or modify the current field depends on the type of data selected.