Organizing and presenting your WordPress blog posts as part of some series make it easier for other readers to discover other similar posts. Like you can use post series for writing a long story into parts or whatever. Organize Series plugin activates a new taxonomy (like categories) for your posts.

Install and activate the plugin then follow the given steps:

1. Navigate to your Dashboard -> Posts -> Manage Series and create your own series just like you create new categories.
2. Now while creating new posts or editing old ones you can easily assign them to some series right from the post’s edit page.

Main Features:

1. You can create new post series
2. You can assign both new and old posts to series
3. Displays all series information in Dashboard’s Right Now widget.
4. Provides you sidebar customizable sidebar widgets for series
5. Clicking the name of series directs you to auto generated TOC for all posts in that series, just like categories.

View its documentation here.