File Explorer, traditionally called Windows Explorer, is designed with a layout that lets a user move between locations and see the contents of the selected location at the same time.
The window is split into two main sections: a navigation pane on one side, listing drives, folders, and shortcuts in a tree structure, and a larger content pane on the other side, showing the files and subfolders contained in whatever location is currently selected in the navigation pane.
Larger numbers describe finer subdivisions some materials use for the toolbar, address bar, and status bar, but the core division that defines how Windows Explorer is structured and used is this two-pane layout, so the smallest number is the one that matches the basic description in the question.
When revising software interfaces, focus on the main functional split (here, navigation versus content) rather than counting every visible toolbar or strip, since exam questions about "how many parts" usually refer to that core structural division.