> For the complete documentation index, see [llms.txt](https://apphp.gitbook.io/artificial-intelligence-with-php/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://apphp.gitbook.io/artificial-intelligence-with-php/neural-networks/overview-of-nn/how-nn-works.md).

# How NN Works

* The process of data flow and transformation through a network.
* Activation functions and their purpose.
* Training neural networks: forward propagation, loss calculation, and backpropagation.