Having in mind that WordPress is one of the most popular web building systems, if not the most popular, there are a lot of plugins you can find for easier management of your WordPress Meta descriptions. Our personal recommendation is to use the WordPress SEO by Yoast.
http://wordpress.org/plugins/wordpress-seo/
You can check more details on how to install plugins to your WordPress from HERE.
WordPress SEO by Yoast is one of the easiest and pretty much self-automated plugins available. This plugin will start working straight out of the box and will apply a lot of optimization for amazing results. Also you get specific SEO fields in each post to make the optimization for each article, post, etc. relate more to it:
Make sure that for each post you use relevant content in the SEO fields .
With only these basic steps you will greatly improve your WordPress Search Engine Optimization and get a better rank!