Switching Between Books
In a series, you're always working in one Book at a time: its chapters, its scenes, its manuscript. Switching Books is designed to be effortless, so hopping from Book 1 to Book 3 to check a detail never breaks your flow. And it's safe: switching automatically saves what you've been working on, so hopping between Books doesn't lose your work. It only changes which Book you're looking at.
The Book Switcher
The navigation bar (the bar at the top of the screen) always shows Current Book: followed by the name of the Book you're in. Click it to open the switcher. Under Switch Book, every Book in your series is listed in order. Click one and you're there. The switcher works the same way in Worldbuilding Mode (your characters, chapters, and notes) and Manuscript Mode (where you write your prose), so you never have to leave the page you're on.
Keyboard Shortcuts
Press Ctrl+Shift+1 through Ctrl+Shift+9 (or Cmd+Shift+1 through 9 on Mac) to jump straight to a Book by its position in the series. The shortcuts appear beside the first nine Books in the switcher, so you never have to memorize them. And if you'd rather use the mouse, clicking a Book in the switcher does exactly the same thing.
Penpoint Remembers Your Place
Each Book keeps its own place on the Chapters page and in the Manuscript, so you pick up right where you left off. Leave Book 1 mid-chapter to check something in Book 2, and when you switch back, Book 1 is exactly where you left it.
Show Only This Book
In Worldbuilding Mode, the This Book / All Books toggle sits right beside the switcher, and at the bottom of the switcher menu the "Show only this Book" checkbox does the same thing. Both hide characters, items, and locations that aren't in the active Book. Nothing is removed, and switching back to All Books (or unticking the box) brings them all right back. It's a quicker way to flip the same setting described in This Book vs All Books, which explains how it works everywhere at once.