Finding quality free materials to start learning machine learning can feel surprisingly easy once you know where to look. I began with the famous 'Python Machine Learning' book, but a friend pointed me to the free HTML version of 'Hands-On Machine Learning with Scikit-Learn, Keras, and TensorFlow' by Aurélien Géron. It's the second edition, available on GitHub. I printed chapters as needed and found the practical, code-first approach helped me grasp concepts that drier texts made opaque. Another absolute cornerstone is Andrew Ng's original Coursera course, which is free to audit. The explanations of foundational math and intuition are unparalleled; it's where things finally clicked about gradient descent.
For a more structured, book-like experience, I'd also recommend 'The Hundred-Page Machine Learning Book' by Andriy Burkov. The full PDF is free from the author's site. It's dense, but it distills the essence of complex topics into something digestible for self-paced study. Honestly, the biggest challenge isn't finding resources, but staying disciplined enough to work through the exercises in Jupyter notebooks. I still have to fight the urge to just passively read.