The next item in the Main view is Bookmarks. Bookmarks are predefined queries with a descriptive name and a shortcut - in the example above, we see the default bookmarks. You can view the list of messages matching a certain bookmark by pressing b followed by the bookmark’s shortcut. If you’d like to edit the bookmarked query first before invoking it, use B.
Bookmarks are stored in the variable
mu4e-bookmarks; you can add your own and/or
replace the default ones; See Bookmarks.