Recommended Tests

I've been trying to use the Telnet application in dos to connect to computers but im having some trouble, everytime i try to connect to a IP address it says Connecting To xxx.xxx.x.x...Could not open connection to the host, on port 23: C
onnect failed. I've tryed multiple IP addresses and same result. Do you need certain port forwarding on your router? Do you need the computer to be on at all times? Any other information would be much appreciated.