Heavenly Stems and Earthly Branches
Heavenly Stem and Earthly Branch are the most useful tool to find people's lucky years in the Chinese Fortune-Telling system. You can find your lucky element (one element from Five Element) from 
Chinese Fortune Calendar and then use your lucky element to find your lucky years. However, Five Elements are actually broken down into Yin and Yang. People's real lucky element maybe is the Yin element or Yang element or both elements. Because the purpose of fortune-telling is to find the TIME for good or bad events, Chinese just use Stem and Branch, the symbol of the Chinese calendar time, directly to find those lucky years. The relationship between Stem-Branch and Five-element can be found in the Five Elements Application Chart.
