Double-breasted men’s suits have a jacket with extended overlapping front flaps and a couple of parallel columns of buttons. Modern double breasted suits have a single column of functional buttons; the other column is decorative.
Traditionally, a double-breasted jacket has six buttons, three of which could be closed. The four-button double breasted jacket is often known as the Kent, being named after the Duke of Kent who made this particular style of men’s suits popular.
Never unbutton a double-breasted jacket while standing; this allows it to flap around and can never look neat. Keep the jacket buttoned while standing and leave it buttoned until you sit down.