To create a monitor, click the "New Monitor" button. To edit an existing monitor, select it in the list and click the "Edit" button. The Monitor Editor sheet will appear:
The IP address is normally set to "127.0.0.1", which is a special IP address that always refers to the computer itself. You should only need to change this if your computer has multiple IP addresses, or your service runs "virtual servers" or is running on a non-standard port. See Choosing a different IP address for more information.
See Types of monitors for information on using monitors.