|google.com.mx Google Doodle on Nov. 2, 2011|
Altars or offerings are set up in homes, churches, schools, etc. They typically include a photo of the person the altar/offering is for (so that the souls can recognize themselves and know where to go), candles and orange marigolds (which are/represent light so that the soul can find its way), flowers or something a purple-ish color (that represents mourning), and favorites foods and drinks of the person. The belief is that the soul cannot taste or consume these items, but can enjoy the aroma -- so the stronger the aroma the better.
Read more about Día de Muertos at http://www.dayofthedead.com and All About Puebla (a great blog about Puebla by a fellow gringa).
You can also visit my posts from last years' Día de Muertos at the UNAM, in the Zócalo, in Coyoacan and in Mixquic.