What is Google Ad Words ?

Google Ad words is a pay- per- click program run by Google.
What this means is that instead of earning positioned as in the natural listings, you can pay to be seen.
Google divides its search engine real estate into two parts:
Natural listings
Sponsored listings
Natural listings as you know cannot be bought, only earned through relevance, so good positions are only achievable by optimizing your website.
By using Google Ad words you will be appearing in the sponsored listings (that are displayed alongside the natural listings) by agreeing to pay if someone clicks on your ads.
At first this sounds are not very cheapest but if managed correctly the costs involved are very reasonable considering the visibility and target traffic you will receive.
You will only have to pay a fee when you receive clicks on your ad. This shows that you will only pay when google sent someone to your URL. The price of your clicks will depends on the industries you are in and the competition building on your desired keywords.
Google Ad words will only be cost effective if setup and managed correctly.