All Projects is the library window. It reads the documents on disk, so there is no private index to fall out of date.
Your Work
Recents lists every document with a thumbnail of its first screen, its screen and board counts, and when it last changed. The + button makes a new document (⌘N).
Tags
Tags such as Shipping Q3, Needs review, and Blocked appear in the sidebar with a count. Click one to filter the grid.
Search
The search field at the top right finds projects and screens by name.