Finch uses conversion tracking to track the details of your campaigns' performance. When you have conversion tracking installed, you know whether a visitor to your site purchased a product or signed up for your newsletter. You also know which of your keywords work the best to lead people to your website. Finch needs this information to determine how much to pay for a click for those keywords in order to maximize sales and minimize costs.
To learn more about conversion tracking, visit http://adwords.google.com/support/agency/bin/answer.py?hl=en&answer=142348.
To learn how to set up AdWords conversion tracking, visit http://adwords.google.com/support/aw/bin/answer.py?hl=en&answer=115794.