Adwords ads with cost-per-click pricing are uniquely useful because :-

Your price is automatically lowered to one cent more than your closest competitor.

No one can lock in the top position. User clickthrough rates and CPC help determine where your ad is shown. The most relevant ads rise to the top.

Google offers a unique set of tools to forecast your budget and select target keywords.

You can target your ads to users in a specific country or only to speakers of a specific language.

Because Google Adwords is the most popular and biggest Pay-Per-Click (PPC) service available on the web, it can turn out to be really competitive too. So choosing the right keyword is really important. Of course, the more competitive a particular keyword is, the more will be its Cost-Per-Click and the harder will it be to get seen on the main Google Search Results Page. As soon as people start clicking on your Adwords Ads though, you'll move up closer to the top position, and traffic will start pouring in giving you bigger profits. So it is very important that you try bidding on lesser competitive keywords in the beginning and for this it is necessary that you do adequate keyword research. To learn more about keyword researching, read the Keyword Research for Google Adwords.