December 26th- December 26th is the first day of Kwanzaa. Kwanzaa is a week-long holiday celebrated throughout the world from December 26th to January 1; it honors African heritage and is marked by the lighting of a kinara or a candle holder.There are seven principles of Kwanzaa, hence seven days of Kwanzaa: 
Umoja-Unity
Kujichagulia-Self-Determination
Ujima-Collective Work and Responsibility
Ujamaa-Cooperative Economics
Nia- Purpose
Kuumba- Creativity
Imani- Faith
Click Here to learn more about the seven principles.
History:An African-American scholar and social activist, Ron Karenga created Kwanzaa in 1966 as the first African-American holiday.Karenga said his goal was to "...give Blacks an alternative to the existing holiday and give Blacks an opportunity to celebrate themselves and history, rather than simply imitate the practice of the dominant society."The name Kwanzaa derives from the Swahili phrase "matunda ya kwanza", meaning "first fruits". The choice of Swahili, an East African language, reflects its status as a symbol of Pan-Africanism, especially in the 1960s.
Picture Source