All of that is easily done with the new Music and TV apps on your Mac and your phone. On the Mac, you can add mp3's to the Music app and mp4's to the TV app by simply dragging them there. If you turn on media sharing, you can access all of these with wifi on your iPhone, iPad, AppleTV and other Macs on your home network. Or if you like, you can sync them with your iPhone/iPad or manually manage them (depending on your settings).
This is how it worked before, but you now would use the TV app, Music app and System Preferences on the Mac whereas before it was all done through iTunes.