Sitemap
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Sitemaps that you submit to Google are usually in XML format:  
See http://www.sitemaps.org/ for details.

They often have a filename of the form: "Sitemap.xml"

And look something like this (source: http://www.sitemaps.org/protocol.html):

    <?xml version="1.0" encoding="UTF-8"?>
    <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
       <url>
          <loc>http://www.example.com/</loc>
          <lastmod>2005-01-01</lastmod>
          <changefreq>monthly</changefreq>
          <priority>0.8</priority>
       </url>
    </urlset> 

These are machine readable, not intended for end users. They simply inform Google about all the pages on your site.

However, Google is reporting that the sitemap you have submitted is in HTML format. Sitemaps for humans to read are usually in HTML.

Duplicate Meta Descriptions
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The cause for this is likely to be a conflict between your SEO plugins. So you need to remove one or both of these, or configure them so they don't output a meta description.

If you have already done this then it can take some time before Google recrawls your site and refreshes these reports. Google won't acknowledge your changes instantly.

As is suggested, the Meta Description should be unique for every page. And should be a short (but not too short) description of what is on that page, not your site as a whole.