A tangihanga usually lasts three days and are held either on marae, or now-a-days, at the person´s house. It is the Maori process of mourning.
Fundamental to this belief is the support for the whanau pani (bereaving family), those that have been left behind and have to deal with the loss of someone they love. People gather to spend time with the whanau pani, to grieve with them and to support them in their time of sorrow. A tangihanga is a chance to re-affirm whanau (family) ties, to meet again with long lost relations, to meet relations that you may never have seen and a chance for the children of that whanau to meet their aunts and uncles.
A tangihanga is not just about grieving, but about saying goodbye. It is about having one last time with the person, to talk to them, to laugh with them (have you ever heard the hard case stories that can come out at a tangihanga about the person?) and to cry for them.
A tangihanga is also about talking to others about the person. The general korero (talk) often revolves around the person. Some people find it hard to talk about their feelings concerning their loss to those that are as close to the person as they are, feeling that the other person is going through the same thing, and they do not want to impose themselves on anyone. However, at a tangihanga there are plenty of people their to share your grief. This is all part of the support at a tangihanga.
Some areas have a Po Whakangakau, or Po Whakamutunga which is the final night. On this night, people perform, sing, tell jokes and generally have a good night of laughter. It is to cheer the whanau pani up, knowing that the next day will be the hardest.
The tupapaku (body) is also not left alone at all during the whole tangihanga. This is so the person has company for their final days on earth, and so that they know they will never be forgotten.