Google WebMaster Tools is part of webmaster central.which is very useful to find out about relation between our site and googlebot.googlebot is a robot which read all the information in internet..Google Webmaster Tool shows traffic for each keyword separately, it give more information about website performance according to Google search query. This tool does not cover search query result from others search engine, such as Bing, Yahoo and Baidu.

this tool provides lot of information like:

1.messages ,if you made in it.
2.site configuration
3.sitemaps,you can add sitemap for your site.
4.crawler access
5.sitelinks,which is shown in SERP(search engine result pages)
6.URL address changes
7.settings(set crawling speed)
8.URL Parameters
9.Search Queries,people search using keywords.
10.links,incoming and outgoing links to your site.
11.traffic resource of your site.
12.google+  statistics +one details

so this is very useful for every webmasters.first add your site URL,and sitemap.trace your site easily..

learn more...http://en.wikipedia.org/wiki/Google_Webmaster_Tools, and http://www.google.com/webmasters/edu/quickstartguide/index.html