Open Lumerical FDTD side-by-side with your PDF. Do not copy-paste scripts initially; type them manually. This forces you to notice syntax details (e.g., set("name","value") versus setnamed ).
Most "top" Lumerical FDTD PDF guides follow a structured learning path that covers: lumerical fdtd tutorial pdf top
Remember, the top Lumerical FDTD user is not the one who has read the most PDFs, but the one who has run the most simulations. Use these PDFs as a scaffold, but always attempt to modify the tutorial examples to fit your own research. Simulate a grating coupler instead of a straight waveguide. Replace silicon with a phase-change material. Break the tutorial on purpose to see what happens. Open Lumerical FDTD side-by-side with your PDF