I highly recommend the video from karpathy https://www.youtube.com/watch?v=VMj-3S1tku0 https://www.youtube.com/watch?v=VMj-3S1tku0 - This explains the same idea

I highly recommend the video from karpathy https://www.youtube.com/watch?v=VMj-3S1tku0 https://www.youtube.com/watch?v=VMj-3S1tku0 - This explains the same idea spelled out in code. It really helped me understand the mathematical expression graph of neural networks. He uses graphviz to show the expressions and initially calculate gradients manually and then implement back propagation.