For example if you know of a select few sites that really cover a specific, a custom search engine lets you focus searches on just those sites. This is an extension of their "site:xyzzy.com" search modifier which limits the search to one site.
There is an example search engine at: http://recipeclues.com/
It is trivial to create a simple search engine. First you must have a Google account, which you can create from the CSE page. Once logged in there is a link named 'New Search Engine' and you'll be taken to a page which makes it very simple to create the search engine. You give a name for the search engine, a couple parameters, and a list of websites. That's it.
You can add more sites, or delete old sites, at any time.
There is an area within the CSE site to manage your search engines. The control panel allows you to do: Basics | Sites | Refinements | Look and feel | Code | Collaboration | Make money | Business Edition | Advanced | Preview
These include:-
- Controlling which sites are in your search engine
- Controlling the look of the search engine results pages
- Host the search engine on your own website. By default the search engine appears on a Google website, but in many cases you'll want to make it look like it's on your own website. I have integrated a custom search engine into http://reiki.7gen.com/ ...
- Share the work, that is collaborating, of maintaining the list of sites in your search engine.
- Display adsense advertising on your search engine results pages, and make money.
- Store the configuration of the search engine on your own server rather than use Google's site to manage the details.