There are three levels of happiness. Physical happiness, emotional happiness and happiness of the spirit.

At the physical level, happiness is simply getting our physical needs met. Temperate environment, satiation of hunger and thirst, lack of pain and suffering.

Emotional happiness is almost always linked to our need for acceptance and appreciation by other living beings. 

Finally, happiness of spirit is linked knowing deep inside that you have not through your free will taken away the physical or emotional happiness of anybody.  Do no evil summarizes the recipe for happiness of the spirit.