When we use Google Adwords PPC to increase traffic and online sales, one often looks at the total clicks and click through rate (CTR). While these metrics do reflect the amount of traffic to your site, what is more important for ecommerce sites is how much of these clicks really translate to sales. This is measured by the conversion rate. Conversion rate alone is not enough to measure the true effectiveness of your Google Adwords campaign. While higher conversion rate does indicate higher online sales, the effectiveness of your Google Adwords campaign is also measured by ROI which is defined as

ROI = Profit per conversion/cost of conversion

Higher conversion rate, coupled with higher ROI means a successful campaign. You can learn a lot about Google Adwords from the following series of Google Adwords Educational Videos from Google.