indeed the most unfamiliar/off-putting part might be the matrix formulation of the designs (and the matching of dimensions), which is not even useful if you are

indeed the most unfamiliar/off-putting part might be the matrix formulation of the designs (and the matching of dimensions), which is not even useful if you are trying to implement a toy example in programming. But you can equally well understand backpropagation by following the updating of a single weight, which is much more intuitive. The other thing is the unfortunate/misleading/atrocious jargon that has been adopted.