The Vietnamese attach great importance to ancestor worship because our grandparents, parents and we are descended from the ancestors. While the grandparents and parents are still alive, the children must take good care of them and heed their advice. After they pass away they are worshipped on the anniversary of their death and Tết holiday. Wedding ceremonies, births and other important events are also announced to the ancestor.
The practice is based on the belief that the soul lives on after death and becomes the protector of its descendants. The Vietnamese accept as a fact their ancestor continue to live in another realm, and it is a duty of the living to meet their needs. In return, the ancestors give advice and bring good fortune.
The custom of ancestor worship is relatively straightforward. Nearly every house, office, and business in Vietnam has a small altar, with photographs of the deceased, to provide a place to commune with the ancestors. Besides on the day of the anniversary feast, incense sticks are burned frequently. Other offerings include great platters of fruit, food, paper money and origami of motorbikes, cars and houses. The paper gifts are burnt so they can ascend to heaven for the ancestors to use. It is not necessary to offer expensive things. It is sometimes a bouquet of flowers and a bowl of water. Sincerity and respect is the most important thing.
Another tradition is the placing of wooden tablets on the altar for each ancestor from recent generations. This is less rigorously observed today, and tablets are often replaced by photographs. The custom of the eldest son customarily arranging the altar and inheriting the family house is still generally observed.
As you keep learning Vietnamese culture, you will see that the effect of ancestor worship upon Vietnamese society is profound. The ancestors are consulted when starting a new business, or whenever a member of the family needs guidance, favor or counsel.