it scans incoming emails for viruses. It must always be up to date to catch the new viruses, and as with any anti virus software, there will be a period from when a new virus appears when then is no protection, until the signature files are available to protect against it.
Open AVG resident shield by double clicking on the icon in the system tray.
Ensure that on resident shield tab all 3 check virus boxes are ticked, and also tick use heuristics as this may help find new virusues or suspicious files.
On the email scanner tab, check all boxes.
If you have broadband set the automatic update to check daily.
Many of the virus infections are now caused by trojans which do not eneter your system via email, but from a web page through an open port on your connection, which is not protected by your AV software. To protect against this you need a firewall.
Sygate, and zone alarm are free for perosnal use and both will protect you. If you have bb and have a router, it should have a hardware firewall to protect you.