How do I configure SSH on OS X?

The SSHD configuration is stored in

/private/etc/ssh/sshd_config

To stop and start SSHD:

sudo launchctl stop com.openssh.sshd
sudo launchctl start com.openssh.sshd

You can restart SSH somewhere in the sharing dialogs, but you don't have to. According to the man page on apple.com keys go to the ~/.ssh/authorized_keys file.

In OS X El Capitan 10.11, sshd_config is in /private/etc/ssh/sshd_config (same as /etc/ssh/sshd_config)