An enagement party is used to share your news in person. You could skip this party and send engagement announcments also. Usually the brides family hosts this party and it can be formal or informal. Usually its best to host a nice brunch or evening cocktails with a very light menu and light refreshments. Personalize the event with napkins for cocktails or small mint tins for brunch. Be sure to ONLY invite those that are invited to the wedding! Also the Bride and Groom should toast to thank everyone for coming and tell them you are looking forward to seeing them at your wedding!