Its really super easy to use, D/L here:http://code.google.com/p/simulationcraft/downloads/list
You'll probably want the Win32 zip unless you are on an Apple.
for Windows just d/l the .zip and open it. Drag the whole folder out to your desktop. It doesn't need to install, just open the folder and click on the "SC" icon in the folder.
Click on the import tab at top and search the armory for your toon. The options tab is the where all the fun is.
Iterations - I usually select 25k for this.
Length - I usually set at 300 with 20% vary or set to 350 with 0% vary.
Style - Patch / Helter / Ultrax - Your choice. The Ultrax is nice for modelling that particular fight though
Threads - I usually give it at least two.
Buffs / Debuffs:
Playing around with these is encouraged. You definitely want to do at least one run with the buffs you generally have in your raid. For example if you don't have a Lock, you can't get DI. But knowing what it would do for your dps if you did have one is good knowledge.
I usually check INT/HASTE/MASTERY/CRIT
Plotting: I have had trouble with plotting taking forever to complete. Try if you want, but I would run a few times without it first.
Hit that Simulate button and let it run.