Phase 2 of 8: Enough ML to understand inference. Week 6 of 32, part 1 of 2. Every week so far, the model already existed. I ran Phi-4, read Qwen's files, and measured tensors, but I never made a model learn anything. This week I build one from scratch and train it. That is a lot for one sitting, so I split the week into two posts and go slowly. The goal: the model starts with a random weight and bias, which are just wrong guesses. Training is what adjusts them, step by step, until...