This lecture covers the techniques and applications of synchrotrons, x-ray free-electron lasers, relaxations, reconstructions, and examples in surface x-ray diffraction. It explains the diffraction intensity, relaxations, reconstructions, and superstructure rods in detail, using examples like the surface of Ru(0001) and graphene on ruthenium. The instructor discusses the in-plane and out-of-plane movements, providing insights into the corrugated moiré pattern and the experimental setup for graphene on ruthenium.