https://brohrer.github.io/how_convolutional_neural_networks_work.html – This page did a good job of breaking down the individual operations that are common to all CNNs – ReLU, pooling, convolution, etc. After reading the article you can basically implement your own CNN – but without a lot of the advanced improvements that have made them faster and more powerful.

https://towardsdatascience.com/review-yolov3-you-only-look-once-object-detection-eab75d7a1ba6 has lots of reviews of algorithms

Dive into deep learning – a free book: http://d2l.ai