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International Tables for Crystallography, Volume H: Powder Diffraction (2019), edited by C. J. Gilmore, J. A. Kaduk, and H. Schenk, DOI: 10.1107/97809553602060000115

This is a comprehensive reference on powder diffraction. If your library does not have a physical copy of this, they may offer on-line access.
Fundamentals of Powder Diffraction and Structural Characterization of Materials (2025), P. Y. Zavalij and V. K. Pecharsky, Pecharsky & Zavalij). Springer, DOI: 10.1007/978-3-031-91504-8
Principles and Applications of Powder Diffraction (2018), A. Clearfield, J. H. Reibenspies and N. Bhuvanesh, Wiley, DOI:10.1002/9781444305487.
Powder Diffraction: Theory and Practice (2008), R. E. Dinnebier and S. J. L. Billinge. Royal Society of Chemistry. DOI: 10.1039/9781847558237-FP011

Any of the above three provide a comprehensive introduction to powder diffraction, with the first two books more aimed at introductory materials, while Dinnebier & Billinge is a collection of chapters written by leading researchers.
X-Ray Diffraction Procedures: For Polycrystalline and Amorphous Materials, 2nd Edition (1974), H. P. Klug and L. E. Alexander. Wiley.

Quite old and very expensive, but still the best discussion of laboratory instruments to my knowledge.
Jeremy Cockcroft provides notes from an on-line powder diffraction course: http://pd.chem.ucl.ac.uk/pd/indexnn.htm