The short answer
Eight Mansions (Ba Zhai) is the most accessible Feng Shui system. From your birth year and gender it derives your Gua (Kua) number, which splits the compass into four auspicious and four inauspicious directions that are personal to you.
The heart of it
Your four good directions each serve a purpose: Sheng Qi (success and wealth), Tian Yi (health and helpful people), Yan Nian (relationships and longevity), and Fu Wei (stability and clarity). The four bad ones range from mild setbacks to total loss.
Why it is worth your attention
Because it needs only a birth year and a compass, Eight Mansions is the quickest win in Feng Shui — a daily alignment you can apply at your desk, your bed and your front door immediately.
Try it yourself: Lucky Directions (Eight Mansions) is free on FengMaster, computed to the letter.