For those who are new to this, you may go to the official Google Webmaster Tools site to create a new Webmaster profile.
Upon logging in using your Gmail account, key in your blog site URL, and click OK. You will then be asked to verify your site. This is to ascertain that you are indeed the owner of the site.
There are two ways to verify your site. You can either add a Meta Tag or Upload an HTML file. If you are using the Meta Tag method, Google will generate a Meta Tag code. Copy the META tag that is generated for you, and paste that between the head tags (go to your Blogger dashboard. Under Design ->Edit HTML)
<Replace this with the code generated by Google Webmaster>
<b:include data='blog' name='all-head-content'/>
After you have had your site verified, click on the Add a Sitemap (Which is in the Sitemaps tab). By adding a Sitemap, you will be providing Google with more details and information about your Blog. With this, Google will crawl your site, report information on any errors in the Sitemaps tab, and index your Blog site at a faster rate.
This will take you to another screen where you should choose the type “Submit a Sitemap”. The Sitemap URL for any normal website is usually the index page that is stored in the highest-level directory of that site. In the case of Blogger.com or Blogspot.com, the only way to add a Sitemap is to use either of the following 2 Sitemaps
http://your blog name.blogspot.com/atom.xml