From Nookipedia, the Animal Crossing wiki
During the Harvest Festival, from 3:00 to 9:00 P.M., Franklin will hide behind obstacles (such as trees and signs) and wait for the player to bring him pieces of silverware from the banquet. In Animal Crossing, the silverware can be taken from the banquet tables near the Wishing Well. In Animal Crossing: City Folk, the silverware can be acquired by speaking to Tortimer by the town hall, who will give the player silverware, thinking that the player will be using it him or herself or will be distributing it to the other villagers. Silverware can be taken multiple times, and for each piece of silverware that Franklin receives, the player will receive one piece of furniture from the Harvest Series (including the wallpaper/carpet). Duplicates may occur, however.
In Animal Crossing: City Folk, the player can give the cutlery set to any villager for a clue as to Franklin's location, but only one clue can be retrieved from each villager per year (ten clues in total).
Franklin is unusual among Animal Crossing residents and visitors in that he is entirely static; unlike the other visitors, such as Saharah or Joan, he does not walk around the town. Instead, Franklin will appear in his hiding place and will disappear soon after the player moves the camera out of view.
While in one hiding place, Franklin will accept only one "knife and fork" set, so to receive more, the player must move away from the hiding place until Franklin disappears and search for him again.
In New Leaf
Franklin appears again, this time as a chef. He will ask for three ingredients (including, but not limited to flour, milk, fish, and fruit) and a fourth, secret ingredient to make the dish better. To receive one of the ingredients (flour, vinegar, milk, butter, or sugar) the player must go around town trading ingredients with their villagers until they get it. Villagers will also give mushrooms or fruit. Villagers only ask for fish (including Sea Bass, Black Bass, Horse Mackerel, Carp, Crucian Carp, and Barbel Steed). After the player gives them the fish they requested, they will offer a hint on the secret ingredient for the dish currently being working on or a potential later dish. Franklin appears at the event plaza. After the player has completed a dish, he rewards a piece of furniture from the Harvest Series or a holiday item. Once the player has given him the ingredients for the final dish, the villagers will stop asking for ingredients.
The secret ingredients can include the following: