Google taking another step towards improving your experience with Google webmaster services with the launch of On-Demand Indexing in Custom Search. With On-Demand Indexing, you can now tell Google about the pages on your websites that are new, or that are important and have changed, and Custom Search will instantly schedule them for crawl, and index and serve them in your CSEs usually within 24 hours, often much faster.

So how can you tell google about your urls? It is very easy. You have to provide a Sitemap to Webmaster Tools, like you always do, and tell Custom Search about it. Just go to the CSE control panel, click on the Indexing tab, select your On-Demand Sitemap, and hit the “Index Now” button. You can tell google which of these URLs are most important to you via the priority and lastmod attributes that you provide in your Sitemap. Each CSE has a number of pages allocated within the On-Demand Index, and with these attributes, you can let google know which are most important for indexing. If you need greater allocation in the On-Demand index, as well as more customization controls, Google Site Search provides a range of options.

Some important points to remember:

• You only need to submit your Sitemaps once in Webmaster Tools. Custom Search will automatically list the Sitemaps submitted via Webmaster Tools and you can decide which Sitemap to select for On-Demand Indexing.
• Your Sitemap needs to be for a website verified in Webmaster Tools, so that we can verify ownership of the right URLs.
• In order for Google to index these additional pages, the crawlers must be able to crawl them. You can use “Webmaster Tools > Crawl Errors > URLs restricted by robots.txt” or check your robots.txt file to ensure that you’re not blocking us from crawling these pages.
• Submitting pages for On-Demand Indexing will not make them appear any faster in the main Google index, or impact ranking on Google.com.

You can further study on it by visiting http://googlewebmastercentral.blogspot.com/2008/11/on-demand-sitemaps-for-custom-search.html