ELI5: How IP addresses work (and how hackers use them to get into systems)

Backstory: 9th grader in Melbourne, computer nerd

I'm interested in learning to (for lack of a better term) hack, as every other 15 year old is, but more in terms of learning what is possible, not using it maliciously (obviously keeping it legal). I've been told to learn a programming language, but have an understanding of networking before that. I've searched but haven't found an ELI5 equivalent which explains it to a newb.