Help Google find our blog posts - repost

Google is not currently finding our blog posts, unless I search for each one by subject line. We have XML Sitemap plugin installed on our site, but it shows errors. Please, that needs a fix. And I didn't know if XML Sitemap replaces Google's Site Verification, or whether that will be needed also. Please let me know if XML Sitemap is enough or if we need both. Please fix both if both are needed. I can obtain the HTML verification file from Google webmaster tools using my Google account.