Rockstar Games has launched the online mode of GTA V on PSN and Xbox LIVE now. After you've loaded the update required for this purpose, you're ready to go.
Furthermore, Rockstar Games revealed some more information about missions, security, virtual currency and many other topics. The official newswire page shows you everything that one needs to know to be prepared for Los Santos: GTA Online Details: Game Day Access Info and More
And we have some more screenshots for you: