What is the best resources to learn Graph Convolutional Neural Networks?

Question

For the past few days, I am trying to learn graph convolutional networks. I saw some of the lectures on youtube. But I can not able to get any clear concept of how those networks are trained. I have a vague understanding of how to perform convolution, but I can not understand how we train them. I want a solid mathematical understanding of graph convolutional networks. So, can anyone please suggest me how to start learning graph convolutional network from start to expert level?