Not to be confused with page templates or post formats, custom post types add an entirely new hierarchy of posts to your site. (And I can see your eyes glazing over so we’ll pull out an example.) Example: Have you ever seen/used a website where they have a Portfolio or Testimonials that seem to be displayed just a little differently to normal posts? Maybe you’ve had a theme before that added a separate little menu to your Dashboard for adding those items, and it takes you to a post editor but that might look a little different as well? Those, right there, are custom post types. With them you create an entirely new object on your site (I’m going with Testimonials here). You can add different pieces of Data to these testimonials, such as who they were written by or what work you carried out for them. You can format them in a way that makes sense, uses those new little details, and keeps every single one looking the same from a style standpoint, with minimal work for the end user.