Google AdWords comes in two editions: "Starter Edition" and "Standard Edition." As Google AdWords explains : with the starter edition you can advertise a single product or service with simplified options. It is recommended for those who are new to Internet advertising. You can at any time graduate to Standard edition. Standard edition allows use of full range of AdWords features and functionality: advanced bidding options, multiple campaigns, conversion tracking, and more. It is recommended for experienced Internet advertisers and medium- or large-sized businesses.
Google adWords provides a comparison between the two editions, distinguishing the two on the basis of number of products, reporting, targeting, cost control, planning tools and site targeting.
"The Starter Edition offers extreme simplicity for new users; the Standard Edition offers an easy interface with many more features at no extra charge. Remember that once you graduate to the improved features of Standard Edition, you can't switch back to the Starter Edition."