This is probably one of the more advanced areas of measuring of your sites performance.
Google allows webmasters and owners to track information that google itself is storing about websites it crawls. The information is vast and can be used to help further target your market and make your site perform better in the SE’s for SERP.
Google allows you to submit directly to google sitemaps of your site for their bots to crawl and index. This is probably one of the most useful tools as it assures you that your site is submitted and all the pages that google should crawl get crawled and hopefully indexed. That is the other very interesting thing is that when it does crawl the sitemap it tells you how many pages are indexed by google. Hopefully the two are the same but if they are not, then you know there are pages to do some work on.
Google also tells you other things about your site. Like do you have duplicate page titles, content, various other sorts of things that it finds as negative about your site. This is usually why some pages are not properly indexed. As an example my Coffee-n-Caffeine.com website had some short meta tags. Not something that was too big a deal on a site with almost 2o0 pages to not have 10 of them properly indexed. However since I found that and I fixed that now all the pages are indexed by google.
Google also provides information about what people are searching for which they have clicked on your link to go to your site from google. This information is invaluable, it shows what people are looking for that leads them to you, and also what they are not finding you for. The details that google provides to the webmasters and owners of sites can be of tremendous value in futhering your SERP and also your market share.
Sparky