Ok, you'll need Ip mapping software, to scan the ports, like Zenmap, what I use. You also need cmd and your targets' Ip. You can trace a website with "ping www.website.com", It'll show you its Ip when it pings it.
Start by entering the Ip into the Zenmap (Or your preferred mapping software) and add /23 after it, this is the port that telnet operates on. Select a quick scan and start the scan. We get an output consisting of lots of processes and ****. Now, find port 23, It should have "Telnet" next to it. If it is closed (In red), you're screwed. They have good security. If it is open, well good.
Go to cmd and type in: "telnet <Their Ip here>". it will ask you to log in. Just use "Owner" as username and leave the password blank. Yaaay, you know have access to their computer through cmd, use mkfile or "echo HACKED! >> Desktop/Hacked.txt".