You can give your search engine a name and description. You can also enter a list of keyword that will be used to tune your search engine results. You can also set specific sites to search, so only those sites defined are searched. Here’s a bit from the Google Blog:
We’re thrilled to tell you that the search for your own search engine is over. Today we are launching the Google Custom Search Engine. As you might imagine, it’s a simple and straightforward product to use and understand. In a matter of minutes you can create a search engine that reflects your knowledge and interests; looks and feels like your own; and, if you choose, you can make money from the traffic you receive through Google’s AdSense program. You can even invite your friends and trusted community members to add to and help build your search engine.
RealClimate has already built this new service into their website. So, head over there if you want to see the thing in action. That site actually worked with Google previous to the launch of Google Custom Search Engine so they could get a nice demonstration put together by the launch day.