Can my system protect me when I am home AND away?

YES!  You will arm your security system "Away" when all occupants have left the property.  That will enable all devices on your system to be activated.  You will arm the system "Stay" when you want to move freely within the property, but you want the perimeter doors protected.  Many people do this when they are in for the night, or when they go to bed.  The motions aren't on, so you can more freely within the premises without setting your system into alarm.