YOU (YaST Online Update) is a part of YaST
that enables you to update SUSE-supported software online. It is part of a larger database that keeps track of what software you have installed, the version, where it is, and much more. You can think of YOU as a combination of Microsoft's Online Update and the Install New Software function found in Windows' control panel.
YOU will only update software maintained in SUSE's database. If you have installed other software not explicitly supported by SUSE, it will not be updated via YOU; you will need to seek updated packages elsewhere. YOU's use is outlined in the Updating Software
An explanation of YaST's Software modules.