How Neural Networks Learn: Weights, Activations, and Backpropagation Explained

A technical breakdown of neural network fundamentals traces the architecture from the earliest single-layer perceptron, invented in 1943, through to modern multi-layer deep networks. The core mechanics involve weighted sums of inputs passed through non-linear activation functions such as ReLU, which allow networks to model complex, non-linear patterns in data. During training, a loss function measures the gap between predicted and actual outputs, and backpropagation calculates how much each weight contributed to that error. Gradient descent then nudges every weight incrementally in the direction that reduces the loss, repeating this loop across many training iterations. A practical PyTorch implementation is used to show how each theoretical concept — linear layers, activation, loss calculation, and weight updates — maps directly to working code.