Tutorials for using Mainstage live.

I'd have to respectfully disagree about just setting up. I think the tutorial (the latest one) delves deeply into setups being mindful of cpu usage (which appears to be the crux of most users issues when performing with it) etc. Depending on what you may use it for there are also tutorials from macprovideo on creating guitar rigs also.

Check youtube there are a few there.

ps. i'm not endorsing macprovideo. i just happen to think the tutorial is very informative and useful.

It depends what you do live. My setup is very simple on the hardware side, but can be quite complex inside MainStage.
My setups include:
Two vocals, one bouzouki, one guitar all controlled through MS
one electric cello plus FX in MS, one MIDI guitar driving three synths in MS plus multi-FX in MS.
All synth settings & multi-FX are controlled from an Evolution UC33 controller.

The hard part is not the live setup - MacBook Pro, Edirol FA101, Roland GI-20, Evolution UC-33 and two powered speakers - but designing the concert interface to use with the different instruments & FX.
Your best starting point will be an analysis of all the equipment you plan to use on stage. Keep asking yourself "Is this item needed? Can I do without it?" A simple lean setup is always more reliable than a complex setup. Try to simplify as much as possible, e.g. only use one keyboard unless it is absolutely essential to use more; try and control sounds & FX with as few MIDI controls as possible.

Many years of teaching have taught me that the best way to learn how to do something is to go & do it.