Most formal RSVP cards follow a similar format. The first line will have an M followed by a long blank line. After writing your name and your partner's name on the top line, check whether you plan to attend or must decline the invitation.
The M on the first line is to signify your title, such as Mr. or Ms.
Most RSVPs also include entree selection choices if you plan to attend the reception. Simply check which entree you (and your guest) would prefer.
When you receive a wedding invitation, it is customary and polite to respond as soon as possible.