An Introduction to Statistical Learning: With Applications in R, Gareth James, Daniela Witten, Trevor Hastie, and Rob Tibshirani, 2013 (Springer) - A highly recommended textbook for beginners in statistical learning, providing a clear explanation of linear regression fundamentals.
CS229 Lecture Notes: Linear Regression, Andrew Ng, 2022 (Stanford University) - Comprehensive lecture notes from a widely recognized machine learning course, covering the mathematical and intuitive basis of linear regression.