malware – spreading RAT/Keylogger over network

I just got into cyber security and one of my fav topic is Malware RAT Keylogger backdoor. I am looking in specific topic but can’t find much about how to spread a RAT over a network?
an example (I want to infect my PC with RAT or keylogger and spread over network automatically, anyone using Windows will be infected)

can you suggest me anything?