sorry, but im newbie when it comes to messing with computers...... but i have a question?

when i open my telnetim useing windows xp prof. and the microsoft telnet client)

i type "o" to open a port...................but what ever i type in, it said: could not open connection to the host on port "": connection failed

so my question is this: what am i doing wrong, i have read some stuff on here about telnet, but cant seem to find a answer to my question.

thanks for your time