Welcome to LQ!
1) SSH is installed by default on OS X. You can connect exactly the same as on any other operating system:
2) OS X uses Sudo, and disables root logins by default. You can execute any command with root privileges by adding sudo before the command, eg:
will run the ls command with root privileges. It will prompt you for your users password. You can get a shell with root privileges using the command "sudo -s" which will prompt you for your users password.
I hope this helps