If you'd like, you can follow the tutorial series on my YouTube channel.
If you're looking for the source code of a specific episode, you can find each part by searching through the commit history. Source code became available after Part 3, I forgot to push the changes for parts 1 & 2.
Goes over how to synchronize player movement over the network.
https://github.com/curtjs/multiplayer-pve/tree/e59eaad5fcce9202d0caa0a261bf1c4b2ee0895f
Goes over how to make a waiting lobby
https://github.com/curtjs/multiplayer-pve/tree/e178df59729ce0b939f3ccbf783da6dc5918ee75
Goes over how to implement shooting
https://github.com/curtjs/multiplayer-pve/tree/b03a4ae892633b743ea72362b10bd5276e0419b5