Folders are used for categorizing and structuring your Storymap tree. Issues and ideas can be organized in folders. And folders can be used to create a top-level structure for your epics and stories.
Unlike epics and stories, a folder is not something you plan and “work on” to get done – it is in a sense equivalent to a folder in a file system. However, folders do accumulate estimates to show how much value and effort is within the folder and they can be described with a description.
Read more about the Storymap to familiarize yourself with the different folders and how they can be used depending on their location.