SEO Yoast plugin will not automatically submit your
sitemap.xml file on different Search Engines.
Its just created a dynamic
sitemap.xml for your site.
You can find your sitemap here
after set up the Yoast you have do the following things.
- Allows robots.txt to crawl your site.
- Dynamically created sitemap should submit to search Engines (Google,bing etc)
when you submit your sitemap to different search engines it will index your file you can check that with their web-master tools.
In Google you can simply find
site:yourdomain.com in the search, it will return Google indexed pages.
Hope it make sense..