Ok - from rereading your original question, I think you’re way misunderstanding the whole thing.
You don’t need to do what you were trying to do to login to your shell account. You need to do that if you’re trying to login from another UNIX or Mac OSX machine and want to login without typing in a password.
In your case, you don’t even have shell access to your user machine, so this won’t work. I think what you really want to do is to enable shell access for that user from the web panel under Users -> Users -> Edit.
By the way, this isn’t really a programming question at all, so I’m moving it to “General Troubleshooting”.
If you still want to understand what that line does, it creates the directory “.ssh” on the remote machine if it doesn’t already exist, then puts the contents of your local ssh public key into .ssh/authorized_keys (on the remote machine) so that you can login without a password.