I have sumbitted my blog in Google Webmaster Tools, but its asking to verify my home through a meta tag or a HTML file. How can I upload these files (sitemap.xml, robots.txt and meta tag or HTML file verification)?
You can verify your blog with Google Webmaster Tools by putting the metatag they want you to use.

Go to your site layout or blog template, go to the HTML edit section and put the tag between <head> and </head> tags.