Google's Machine Learning Crash Course has been a quiet staple for years, and the version available now is much better than the one a lot of people remember. Google rebuilt it fairly recently and the update matters, because the old version stopped just as the interesting parts of modern AI were getting going. The current course still teaches the core foundations properly, linear and logistic regression, loss and gradient descent, generalisation, overfitting and how to think about training data, but it now carries through to the things people actually care about today, including embeddings, neural networks and a real treatment of large language models. What sets it apart from the endless supply of free AI content is the quality of the explanations and the interactivity.
This is made by the people who teach machine learning inside Google, and it shows in how carefully concepts are introduced. The interactive visualisations, where you can drag parameters around and watch a model respond, do more to build intuition in a few minutes than a long lecture would. The exercises are real, not decorative, and you come out having actually reasoned about the material rather than just watched it. The trade-off is that this is a proper course and it treats you like a learner, not a tourist.
You will get far more out of it if you are comfortable reading a little Python and you are not scared off by some light maths, and a few of the sections are genuinely dense and reward a second pass. The exercises also lean on TensorFlow and Google's own tooling, which is fine but worth knowing. The certificate, such as it is, carries no real weight, so do this for the understanding and not for a line on your CV. My take is that this is one of the highest-value free resources in the entire space.
If you are past the absolute beginner stage and you want to understand how machine learning works rather than just which buttons to press, I would run through this before spending a penny on a paid program, because it will make everything you do afterwards make more sense.