Monitoring is supplied through the manufacturer of the inverter. There are generally two types of monitoring available for residential systems, system level and panel level. System level monitoring tells you the output, status, etc. of the entire system. So if one panel is not working properly you might notice a slight decrease in output, but it would be harder to detect a small issue in a particular panel. Panel level monitoring on the other hand shows the output, status, etc. of each individual solar panel. So if one panel is having an issue, the monitoring system tells you exactly which panel. This can be very useful for trouble shooting an issue and to ensure that all your panels are working properly.
I've included here a link to an example site that uses panel level monitoring: