Answer:
The seven candles are apart of Kwanzaa because it is apart of the tradition.
When lighting the kinara: the black candle on the first night, the black one plus the leftmost red one on the next night, those two plus the rightmost green one on the next, etc. Each candle represents one of Kwanzaa's seven principles (nguzo saba).
The daily principles include: umoja (unity), kujichagulia (self-determination), ujima (collective work and responsibility), ujamaa (cooperative economics), nia (purpose), kuumba (creativity), and imani (faith). Hope this helps!