My personal favortite:
Neural networks and deep learning[
^]
I worked through his whole article and my Feeling is, he does describe everything very simple and very good.
Give it a Trial. To understand it you should know what Derivate of a function means and at least you should have an Imagination what partial derivatives are.
Don't be afraid from the formulas he explains. Most of them are really easy to understand - even I was able to understand them... but it took some time and discipline.
I started with Zero knowledge and end with "my" c# implementation of his example of OCR... and was very impressed "how easy" such a big Task like OCR can be solved ;)
There is also a very helpfull specific article in CP about ANN.
Not 100% sure it must have been this:
Neural Networks on C#[
^]. It is maybe not an efficient implementation, but what I rememeber it is something General/univerisal.
Good luck.