In the KAT, if you accept the default when prompted for a place to connect to, it will attempt to connect to a router on a hosting service in Madison, WI. f you instead clear out the address so that you're just entering a blank address, the KAT will start a router for each of the predefined worlds on your local machine, and you will just connect to yourself. A few of the worlds will be empty. Some run scripts that create the worlds with some demo content. Congratulations, you've just set up your machine as a “host”. If that box happens to be at a fixed IP address, you can tell other people to enter that address when prompted, and they will connect to you.