a.*?$ into the regex pane, and type the sentence "A man's gotta do what a man's gotta do." into the target pane. Make sure you hit the RETURN key before what so that the panes look like in the screen shot below.
Now try all eight different combinations of the "i", "m", and "s" modifier checkboxes and see how the match changes accordingly. Make sure you understand what happens and why... :)