Updating means updating the virus signature file (the file that detects viruses and other threats) as well as the program itself.
Updates can be carried out on a daily basis either automatically or manually. If you have configured the program to update itself when necessary (automatic update), the program will always be up-to-date. The program will update itself when it detects a connection to Internet, when necessary.
In order to know how up-to-date the program is, In the Updates panel of the main screen you can see the date of the last update.
You can also find out how up-to-date the program is through the icon in the Windows taskbar (next to the system clock). If this icon appears and you place the mouse pointer over it, the date that the program was last updated will be displayed.
For further information consult the What is an update? section in this Help.