There are many things that can be said about the altar or ofrenda at the Day of the Dead, but I thought I would summarize some of the basic ideas below....
The Offering or Ofrenda
The ofrenda is essentially an altar of food and flowers for the dead. It is meant to honor those who have passed.
The predominant flower is the vivid orange and yellow of the cempasuchil (sem-pa-soo-cheel), the flower of the dead, or marigold.
Its colour and aromatic scent are thought to attract the souls toward the altar.
Paths of marigold petals are strewn from the ofrenda to the door of the house to guide the souls to their feast.
The scent of copal incense also invites the souls to enter. See right front of ofrenda--brass plate with 'black copal'.
Above the ofrendas table there is often an arch which may symbolize the heavens or the journey to the afterlife.
The ofrenda itself is usually in three tiers, the first holding an image of the deceased, the second with sugar skulls and playful skeletons (calacas), and the third with the feast of bread, fruit, and favorite foods.
The foods represent the earth. The flame of candles represent fire, and the fluttering of the punched paper banners (papel picado) represents wind.
A towel and water (and perhaps soap or perfume) is set out to refresh the returning soul.
Salt is also placed at the altar for purification of the offering. See front left of ofrenda.
The use of the colors orange, purple, and pink is common. Purple may represent pain for the one who has passed, but some say it, along with pink and orange, signify the joyful return of the spirit. White is also used to represent hope.
The overall feeling is respect for the departed and for the cycle of life. As part of this cycle, the souls return during the Days of the Dead.
Along with this profound respect for the dead is a light-hearted look at death. The sugar skulls, calacas, and especially the image of Catrina , poke fun at Death, saying, "You can't take it with you."
Even as death is a sobering thing, Dia de los Muertos is a time to remember that death and life are intertwined with an attitude of peace, reflection, and even joy.