Anti Virus software is a shield which protect your computer from harmful viruses.
My advice on antivirus program is that every computer must have an antivirus in it to protect your computer from virus.
The things which you consider after installing antivirus that: -
Make your antivirus up to date to work properly in your computer and do not uninstall or off antivirus from your computer.
Before you put an pendrive in your computer make sure that you haved scanned your pendrive with antivirus to delete or repair viruses from your pendrive.
Scan your computers weekly with your antivirus to prevent it from virus.
If you all follow my advice you can know all things about properly using of antivirus software.