A good book about the theory behind neural network: https://www.deeplearningbook.org/
A good introductionary video to matematic behind deep learning by 3 blue 1 brown: https://www.youtube.com/watch?v=aircAruvnKk
Modern object detection use a CNN (Convolutional Neural Network) type neural network.
The club use a technique call reinforcement learning, this technique consist of training an existing model with a new dataset.
A good database of existing model is the model_zoo models: https://github.com/tensorflow/models/blob/master/research/object_detection/g3doc/tf1_detection_zoo.md