What BaZi actually is, where it came from, and what it reads.
'Saju' (四柱) means the four pillars of your birth — year, month, day, hour. Each pillar pairs one Heaven character (a stem) with one Earth character (a branch), so there are eight characters (palja) in all. That's why it's often called 'Saju Palja' (eight characters). Those eight characters are like a snapshot of the energy of heaven and earth at the moment you were born.
How is it worked out? Old East Asia recorded time by pairing the 10 Heavenly Stems and 12 Earthly Branches (the sixty-term cycle). This year, for instance, is called 'Gapjin.' Draw the exact stem-branch pair for the year, month, day, and hour you were born, and that becomes your chart. It's something anyone can work out with just a Ten Thousand Year Calendar (a stem-branch calendar) — a calendar calculation, not a mystery.
The root of it is Yin-Yang and the Five Elements (陰陽五行) thought — an ancient natural philosophy that reads the world through yin and yang and the Five Elements. BaZi is what you get when you attach 'a person's life' to that. The Tang-dynasty scholar Li Xuzhong read charts mainly through the year, month, and day; the Song-dynasty scholar Xu Ziping (徐子平) completed today's framework by placing 'the Day Master (the Heaven character of your birth day) = yourself' at the center and adding the hour. That's why BaZi is also called 'Ziping Theory (子平命理)' after his name.
So what does BaZi actually read?
To sum up, BaZi isn't a tool that stamps out a 'fixed fate.' It's closer to a compass that lays out the map of your born energies and reads where you're strong and what's worth filling in. The first step is the next chapter — the five energies, the Five Elements.
This content is for reference and entertainment, based on traditional Chinese metaphysics and astrology.