Re: what is Ad rotation?
I would like to add bit more information about Adwords ad rotation.
If you choose any of the first two options (optimize for clicks/optimize for conversions) the ad rotation will be decided by Adwords system based on results (Clicks/Conversions).
This may not be an ideal choice every time. For example an ad which gets more clicks may not be the best when you consider conversions. So if you choose the default option (optimize for clicks) and the system starts to show the ad which gets more number of clicks more often, that may not help you to maintain your ROI, because you may be losing conversions just because of your ad rotation setting.
If you want to test all your ads by giving them equal opportunity to perform, without any other influence (clicks/conversions) then you need to choose any of the last two options. You can take ad optimization decisions latter after observation and analysis, based on profitability/ROI.