The napkin has several roles when used during a formal dinner.
1) When the host or hostess places the napkin on her lap, the meal has begun. Guests should also place their napkin on their lap at this time.
2) The napkin is used to catch crumbs and wipe our hands on.
3) The napkin is used to dab, not wipe, our mouths.
4) When the host or hostess places the napkin to left of his or her plate, it signifies the meal is over.