This is a tutorial i wrote for Tuts+ Network
One of the core feature provided by WordPress in extending its functionality is its Meta Box API. These meta boxes enable you to easily add additional data to your content. For example, the Post Tags meta box enables you set tags for your post.
In the tutorial, you will learn how to build a basic SEO plugin that adds a meta description, and an Open Graph title and description tag to the head element of WordPress pages. In doing this, we’ll also learn how to create a custom meta boxes, how to sanitize user-provided data, how to save the data to a post or page, and how to and retrieve the saved data.
Read the full tutorial => Using WordPress Meta Boxes to Build a Basic SEO Plugin