"Generate a step-by-step graphical representation of Zeeman splitting, assuming no prior knowledge of the phenomenon. Begin by illustrating the energy levels of electrons or nuclear spins in the absence of a magnetic field. Progressively introduce the external magnetic field and visually demonstrate how it influences the energy levels, causing them to split. Clearly depict the resulting sub-levels and their relationship to the strength and direction of the magnetic field. Include annotations or descriptions to explain the concept and significance of Zeeman splitting. Aim for a beginner-friendly, educational illustration that guides through the process of understanding and graphically representing Zeeman splitting from first principles."