Ethical hacking. Pentesting. Penetration testing. Call it what you like. It means trying to hack into a computer or network (normally your own) in order to learn about how it works and to try to identify weaknesses.
If you have more than 1 computer on your network, or indeed if you have other devices such as routers, printers, cameras, scanners, IoT devices and so on, pentesting is a fun way to learn stuff and explore. And because you're doing it on a network that you own, it's perfectly legal.
Traditionally, ethical hackers use Linux to undertake their work, and specifically a security-oriented distribution called Kali. But Kali Linux is not for the faint-hearted. So if you're quite technical and want to learn ethical hacking, but from a Windows base, here's a really useful download.
Pentest Box is a portable pentesting environment for Windows. It comprises almost 2 GB of pre-installed, pre-configured, portable command-line tools for exploring security on computers and networks. Just download it, then run the installer and it'll copy all the files to your hard drive ready to use from a special console window.
If commands like nmap and aircrack mean nothing to you, then Pentest Box is probably not for you. But if they mean something, or you want to learn more, check out the product. It's completely free.
Note that Pentest Box may trigger your antivirus program, because some of the tools it contains are designed to circumvent security. The system will still function without those files, so just accept the action of your antivirus program and continue as normal. The product itself is perfectly clean and is safe to use.