Google Webmaster is the service offered by Google to facilitate a website owner to add his website in Google Index.
Google Webmaster requires you to authenticate your website e.g. prove that you are the owner of the website. Once your website is authenticated by you and Google Webmaster, you are allowed to update Google Bot about your website. Google Bot is the Crawler which is constantly crawling the internet for websites and its data.
Google Webmaster helps both Google and website owner.
Google Webmaster helps Google to know more about your website. You as a website owner can tell Google through Webmaster :
# The Website Links and Various Pages both by the help of sitemap.xml and robots.txt.
# The crawl rate for the Google Bot.
# The frequency of change of the Website pages.
# Any specific Country which the website owner wants to track.
# The URL or pages not to crawl.
Similarly Google Webmaster helps a website Owner by keeping him informed about :
# Total number of external websites linking to your website and to which pages.
# Various Search Queries for which your website got impression and at which Rank.
# The Keywords and their weightage for your website.
# Any particular Crawl errors or Malware found in your website.
# Duplicate, missing meta entries which might be affecting your Ranking
# Your Page speed or how fast your website loads.
# Any social activity including G+ clicks your website got.
There are other Webmaster Tools, Google webmaster guidelines in Google Webmaster which is beneficial to both Google and Website owner. If you are not using Google Webmaster, start using now and see the affect in your website Traffic.