Just like any database application, you can select (filter) specific categories of items to display.
clicking this button lets you specify the text select argument applied to the description and amount fields of the display.
clicking this button picks up and applies the select argument from the currently highlighted display line as follows:
If you select the display line by clicking in the statement column, all items having the same statement number will be selected.
If you select the display line by clicking in the reference column, all items having the same reference will be selected.
If you select the display line by clicking in the date column, all items having the same date will be selected.
If you select the display line by clicking in the description column, all items having the same description will be selected.
If you select the display line by clicking in the amount column, all items having the same amount will be selected.
clicking this button will restore all deselected items.
If you find yourself unsure of what you have selected / deselected, clicking the 
refresh display button will regenerate the full display.