Notes and frontmatter
Notes are for your planning, frontmatter is for publishing dedications and maps.
Story notes
Story notes don't count towards your story or goal word count. This is where you can keep all of your worldbuilding notes, character profiles, plot outlines, and anything else you want.
You have the full rich-text editor (minus the highlight function) and can create as many notes as you need.
Frontmatter
These function in the same way as story notes, except they're actually published with the story when you export it or publish it to the library.
Use frontmatter for your dedications, copyright information, world maps, character lists, whatever you need.