I need some clarification for your question. Are you talking about the Kernel Density tool in Spatial Analyst? Or our ESDA tools? Or Kernel Interpolation in Geostatistical Analyst?
Can you link to the help topic that you're having trouble understanding?
This page has a list of our seven ESDA tools. I'm still not sure which one you're talking about.
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00310000000m000000.htm