Say I wanted to get into my friends computer is this what i use to do that, what do i have to do?I know this is against the law
It depends on what services he has running to allow access. If he has SSH running, you can use it. If he has telnet or rlogin or raw open, then yes, you can use this. (PuTTY)

You are going to need usernames and passwords anyway. The method of gaining usernames and passwords can be illegal depending on method used. It'd be much easier to just ask him for access... if you really need it. Even if you do get usernames and passwords, you still need permission.

It is against the law if you don't have permission.

Oh, on what to do... simply type in the ip or url of desired connection. Then choose the server type or port. Then usename. It'll prompt you for a password. You can also read the PuTTY documentation. It'll explain that much better than I have.