In the beginning, there was the Google (SOAP) Search API. In December 2006, Google no longer issued any new keys for this API. Those with keys already could still use the API, but it was effectively deprecated.
The example search given in the Documentation should give you a quick sense of how to use this part of the API. The following command
returns a JSON object, which you can Parse for titles, URLs, and short blurbs.
In order words, we've come from a SOAP based search API that was limited to personal, non-commercial use that nonetheless wasn't tied to web applications to the current manifestation of an Ajax and RESTful API that is open for restricted commercial use tied to displaying search results on the Web. What's next?