Sitemap is a collective list of pages of your website or blog, which could easily be accessed by visitors to your website and crawled by search engines. Having a sitemap would increase the traffic to your site and ensure that search engine spiders do crawl each page on your site.
Creating a sitemap is now simple and do not require any technical knowledge. There are many free sitemap generator tools to help you create a site map for your website. A site map could be created in XML (.xml), HTML (.html) and Text (.txt) formats. Once created, it could be submitted to all the popular search engines. You can either submit the sitemap individually to each search engine or use a Search Engines Sitemap Submitter.
Wordpress blogs do provide plugins to upload your website sitemap file. But in blogger blogs, there is no such option. So for blogger blogs, you could use your blog feed url ( that is if you do have a blog feed) to submit the sitemap to a search engine sitemap submitter like the one mentioned above.
Your xml file to be submitted should be like the below format --
yourblog.blogspot.com/atom.xml
OR
yourblog.blogspot.com/rss.xml
Remember to only submit your sitemap just once a day or it would be treated as spam.