The fact that it's got full Manual mode doesn't mean you *need* to use it for every picture!
The only time you really *need* to venture in to the Manual modes (Av, Tv and M) are when you are trying to achieve a specific effect like controlling the Depth Of Field (DOF)*, or taking pictures in less-than-optimum conditions (like indoors or in the dark).
AV and TV aren't actually manual modes they are aperture priority and shutter priority..
For a concert (or an indoor Disney show like Beauty and the Beast or Nemo: The Musical), I've had decent luck with the following settings: switch to Av mode and select the smallest aperture possible (2.7 at wide or 3.5 at zoom), switch the Metering to Spot, and the ISO to 400.
2.8 although the smallest number is actually the largest aperture..
Make sure you 'pre-focus' (half-press the shutter button) while aiming at the brightest area of the subject and you'll probably get shutter speeds of 1/40 or 1/60 ... *just* fast enough to freeze people on stage if they aren't moving too much. The IS will help, but I'd also recommend switching to Continuous mode, and taking as many shots as you can; some will be sharper than others.
The manual will make it clear how to set the settings I'm talking about, but it doesn't do much for "use these settings in these conditions" -- however, there are lots of those sorts of discussions in the S3 "family" thread.
* not that you have *that* much control, as it is a small-sensor camera.