Custom Search Engines (CSEs) enable you to create Google-powered customized search experiences for your sites. You can search over one or more sites customize the look and feel to match your site, and even make money with AdSense for Search. Now it’s even easier to get started directly from Webmaster Tools.
If you’ve never created a CSE, just click on the “Custom Search” link in the Labs section and we’ll automatically create a default CSE that searches just your site. You can do some basic configuring or immediately get the code snippet to add your new CSE to your site. You can always continue on to the full CSE control panel for more advanced settings.
Once you’ve created your CSE (or if you already had one), clicking the “Custom Search” link in Labs will allow you to manage your CSEs without leaving Webmaster Tools.
We hope these new features make it easier for you to help users search your site. If you have any questions, please post them in our Webmaster Help Forum or the Custom Search Help Forum.
Reference link:http://googlewebmastercentral.blogspot.com/2011/10/create-and-manage-custom-search-engines.html