Well, I've been doing a few researches.
I still can't let go of the fact that you can hack with only someone's IP.

Well, I have two computers at home.
I used my COMP* to port scan COMP2.

I found one open port,
and tried to connect to it.
I was 'forcefully rejected.'

I found another port, and connected to it.
I got:
"Connected.
-ERR AVG POP* Proxy Server: Cannot connect to the mail server!
Connection Closed."

So I quit AVG and tried again to the same port.
Same problem.

I connected to another port.
I was successfully connected.

The program I used was 'Net Tools 5'
Under Start-Network Tools-Connection Analysator and protector
When you start it up,
it says:
Port Connecter and data transfer

My question is:
Does anyone know what to do after connecting to the computer?