WordPress stores all the content in MySql database. Whenever a user visits your web site(or blog), for a basic theme without any active plugins WordPress makes atleast 16 database queries to display the content. With more number of plugins and advanced functionalities in themes, the number of databse queries will increase. This problem gets worse when there is significant traffic for your web site.
To overcome this problem, you can use WP super cache. This plugin generates static html files from your dynamic WordPress blog. After a html file is generated your webserver will serve that file instead of processing the comparatively heavier and more expensive WordPress PHP scripts (ref: http://wordpress.org/extend/plugins/wp-super-cache/ )
You can download WP minify from http://wordpress.org/extend/plugins/wp-minify/ and WP super cache from http://wordpress.org/extend/plugins/wp-super-cache/
Note: After activating the supercache and minify plugins, you need to configure the plugin settings correctly to achieve the desired results.
If you have any questions then feel free to comment or mail me to wordpressconversion