Mina Himwich of Princeton's PCTS continues a three-part introduction to celestial holography, delivered as part of the Institute for Advanced Study's Prospects in Theoretical Physics program. This installment builds on earlier sessions to develop the technical machinery connecting scattering amplitudes in flat spacetime to a conformal field theory living on the celestial sphere at the boundary of that spacetime. Himwich works through the formal structure linking bulk physics to boundary correlators, a central idea in current attempts to extend holographic duality beyond the anti-de Sitter setting where it was first understood. The talk is aimed at researchers and advanced students already versed in quantum field theory and general relativity, assuming familiarity with the earlier parts of the series. It runs long enough to develop real calculations rather than just motivate the subject, reflecting its origin as a working session for theoretical physicists rather than a general-audience talk.