I'm trying to avoid sounding like Chicken Little here, but this article makes these actions very accessible. If you're someone who is just getting started toying with networks and security, it's likely that you haven't thought through what can happen if something you try actually works.
Nmap has a great page that discusses the ins-and-outs of the civil and legal issues involved with port scanning (a related activity). However, keep in mind that the guide linked here goes well beyond port scanning in to actually attempting, and presumably, gaining access to someone else's network. While the legality of port scanning is ambiguous, accessing someone else's network is not. If you land on the wrong guy's lawn, you can end up in a very expensive, and potentially dangerous place.