Folders are a way to group sub-calendars and to create an organizational hierarchy for them. Folder organization makes it easier to find the sub-calendars you are looking for, or to work with only a group of sub-calendars.
The folders have a gray color bar to set them apart from the color-coded sub-calendars.
To create sub-calendars inside of a folder, use a bracket > in this format: Name of Folder > Name of Sub-Calendar.
For every sub-calendar you want in the folder, use the same format and the same folder name.You can create nested folders: Folder 1 > Folder 2 > Sub-Calendar.
To remove a sub-calendar from a folder, alter the name of the sub-calendar by removing the Name of Folder > from it. Instead of Name of Folder > Name of Sub-Calendar, you will have only Name of Sub-Calendar.
Folders allow you to easily toggle the visibility of a group of sub-calendars.
More details about organizing with folders.