Once you have configured your services, you may want to be alerted, e.g. by email, when warning or critical conditions are reached
Load http://nagiosserver/nagios
Choose 'Status Overview' or 'Status Summary' from the sidebar
Click on hostgroup name (fionavar in this case)
Click 'Enable notifications for all hosts in this hostgroup'
Click 'Commit'
Now the notifications defined in contacts.cfg and services.cfg will be active (e.g. email, pager on reaching critical status)