Newbie to EFILive, Just a Few Dumb Questons

Hello,
I am new to using EFI Live V2. I purchased the V2 FlashScan with Tuning and I'm considering the V2 Interface upgrade. I've had the V4 software for awhile now and its working great. I am very familiar with SCT's Advantage III software for Ford. I haven't had much experience using the SCT with GM stuff and I haven't gotten into using my EFI live at all yet (which, I hate to have to admit), but I hope to use it soon. I have a 2001 WS6 with heads and cam that was originally tuned using LS1 Edit to play with. I wanted to copy the tune and do some general enhancements to it. I don't think the guys that tuned it did much with drive-ablity stuff and I think the car has more in it as far as WOT performance. I really just wanted to use the car to get my feet wet with the EFI Live software.
As far as general questions go .... I wanted to know what is a Custom Operating System and when should you use it? Is the COS like a Full Re-flash as opposed to just a recalibration flash? Which one should you use? What can be done with a COS that can't be done with a recal flash? My questions are based on the little experience that I have with the GM SCT software. What are the differences between the different COS's, ie- COS3, COS5 etc ...? I know, my newbie-ness must be funny to you guys who know this stuff well. Any help or general basic knowledge on getting started would be appreciated.

Thanks

No problem- we all had these problems before-

read this link-http://forum.efilive.com/showthread.php?t=7867

i found it very helpful- i mean u got to start somehere-

Thanks

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