You can specify IIS websites by index number (also called the Identifier, can be seen under the Web Sites option in the IIS Manager application) or by name (also called the Description.)
To connect to the server and update the list of available web site names, click "Connect and update." Alternatively, just type a name into the combo box.
The "Fail if already..." checkbox allows you to specify whether some actions will abort if a given action (ie stopping or starting a web site) has already been taken.