As you would expect, Google AdWords plays nicely with Analytics, and allows you to automatically track campaign details in Analytics. It means that the cost per click data, advert variations, keywords, and the fact that the visits are paid for, will show up in your Google Analytics reports under traffic sources.
This feature is called auto tagging, and you need to enable it in AdWords, and link your account to your Google Analytics account for it to work.
AdWords will then add a unique reference number on the end of the links in your adverts, so that when a user clicks on one of them, Google Analytics receives the data.
You might need to disable the feature, because sometimes if you’re website uses 3rd party redirects, or encoded urls, this extra parameter will result in a broken link. However, your traffic will appear as Google Organic, so it’s best avoided.