By default WordPress provides you one H1 heading title field. This tutorial is on a simple WordPress plugin that lets you add sub-headings in your WordPress blog posts and post types.
Installation & Usage: Install and activate SubHeading plugin. After activation the plugin adds a custom field and allow sub titles (headings) to your posts and post types including pages and custom post types.
Its custom subheading field is re-positioned so it is right below the main heading when editing.
By default the plugin appends subheadings to your blog’s RSS feeds and the admin edit post/page lists etc but you can modify this from its admin options page in Dashboard -> Settings -> Reading page.