The traditional way to respond, or RSVP, to an invitation is to use the same wording as the invitation itself, but substituting the names of the hosts for the attendees. It is especially recommended to repeat back the date and time, to confirm these details.
An invitation might use the following text, "Mr. and Mrs. Party Hosters request the pleasure of your company at their cocktail party on Saturday, June 13, at 8 o'clock. RSVP."
Traditional etiquette would dictate that the wording for an RSVP, which is an abbreviation of the French phrase "Respondez s'il vous plait," meaning "please reply," might run as follows: "Mr. and Mrs. Party Goers accept with pleasure the generous invitation of Mr. and Mrs. Party Hosters, to their party on Saturday, June 13, at 8 o'clock."