OpenIntro Statistics, David M Diez, Christopher D Barr, Mine Çetinkaya-Rundel, 2019 (OpenIntro) - A widely used, free, and high-quality textbook covering fundamental statistical concepts, including populations, samples, and sampling methods.
Introduction to Probability and Statistics (18.05SC), Dr. Jennifer French Kamrin, Dr. Jeremy Orloff, 2013 (MIT OpenCourseWare) - Provides academic lectures and materials on probability and statistics, including definitions and relationships between populations and samples.