Google webmaster Tool is a best tool for webmasters to do lots of stuffs regarding their website to make it searchable and visible in Google Search Engine at present time. To get listed in Google search engine, following are the important factors involved with your website.
Sitemap: Generally when ever you search about any specific website in Google search engine,then they will display some special pages link below the website link searched in the search result. It is based on your most viewed or accessed page overall by visitors. Sitemap helps search engine to present your website in front of visitor .

In the above Image, You can see the extra hyperlink added just below the Google.Com. It is due to the sitemap and it is the list of most viewed pages.
Robots.txt: It will tell the search engine about the content of your website, which part of your website you want to stored by search engine crawlers. They will simply include or exclude the pages or directories specified by you in robots.txt file.
Meta Verification tag or file: Meta verification file is very much important for search engine. It informs the crawlers about the latest update or content added on your website. Then they visit your website and stores the updated or newly added content and then they will display it to the Google users in search engine based on your content priority.
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Google Webmasters tool is very eas to setup and use and there will never be an alternative to it