Either that, or the Ovi Store icon, or type in URL store.ovi.mobi in browser, they should all work. Then click on games, find Angry Birds on the list, click it, then click Install (or was it Download) on the page: it launches AppMgr which thinks for a while and then installs the game for you like any other app.

The only difference to Extras is that you have to browse Ovi Store via browser to install stuff, instead of finding apps in AppMgr.