Let me put it this way: an IP address is like a person's home address. After you know it, you want to go to his place and have a look. At this point you've followed the IP (address) to his front door, but how do you get in? There are many ways. The legal way is to call from outside the door: "XXX, buddy, I came to see you!" Then he happily jumps out to welcome you (shared resources), and then you two can communicate; there are many illegal ways in, of course. It's best if nobody is home, or if the person there has problems with their ears or eyes (doesn't pay attention to security), then you can break the door down or pry open a window and get in (making use of network vulnerabilities or hacker tools); of course, at that point you need patience, confidence, and even more time and energy, plus enough networking knowledge. The key is that you have to be prepared to be invited by Uncle Police to the station for dinner, hehe
Intrusion is a very uninteresting but creative thing. It's best to be like me and intrude into your own system; your own family won't shut their own family out, hehe
Read more material on hacking and network security, and wish you success!