You want search engines to index your blog pages but not the PHP files of your WordPress installation. Edit the robots.txt file and add the following lines to block search engines from indexing these files:
User-agent: *
Disallow: /wp-admin/
Disallow: /wp-includes/
Disallow: /wp-content/plugins/
Disallow: /wp-content/themes/
Disallow: /feed/
Disallow: */feed/For more on managing search engine access, see Create and Send a Sitemap for WordPress SEO.