Its not increase your keyword ranking but it show you all important stats or error that help you to make your website much more search engine friendly. And when you have done this all (fix error of your site, placing title on each pages) then this will help your site keywords ranking on search engines.
Google Webmaster tools will help you and your website by providing you indepth statistics, crawl errors and any possible errors with your website or functionality of your website and the ways to fix it so that your users and guests of your website get the best user experience of the site and thus lowering the overall bounce % rate per person. In Short: This helps you as following the information provided by Google webmaster tools will help attain and grasp user experience of your website.
Through Google Webmasters Tools, You will check your website health means the information regarding crawl, index, sitemaps and search queries on each keywords toward your website. If Google will find any malware virus on your website, they will inform you by messages option in your webmaster tools.