Google webmaster tool is a very good and interesting tool for the webmaster.It is also a powerful tool for SEO.
By this tool u can check some important technical issues of ur site and will get the review report to diagnosis it.
There is also a diagnostic tool by which u can get the report if there any error of crawling the google bot to ur site.
By content analysis u can analyse ur meta tags whether they are perfect according to google's rule.


Inside google webmaster tool there is a statistics report.Following statistics report u can

find here :
Top search queries

What Googlebot sees

Crawl stats

Index stats

Subscriber stats

By link analysis u can get a report for the following term:
Pages with external links

Pages with internal links

Sitelinks




Sitemap tools help u to submit ur sitemap to google.

There is also a option called Tool that wll help u to find the following info:

Analyze robots.txt

Generate robots.txt

Manage site verification

Remove URLs

Enhance 404 pages

Gadgets


some days ago i found that google has indexed some php error pages of my site.
i was anxious about that and trying to remove them from search result.I found that i can do it easily with webmaster tool.There is a option to request to remove any page of ur site from search result.