(A)The Toolbar provides access to your Unity Account, Unity Cloud Services, and Unity Collaborate, the play, pause and step controls, and Unity Search, a layer visibility menu, and the Editor layout menu (which provides some alternate layouts for the Editor windows, and allows you to save your own custom layouts).
(B)The Hierarchy window is a hierarchical text representation of every GameObject in the Scene. Each item in the Scene has an entry in the hierarchy, so the two windows are inherently linked. The hierarchy reveals the structure of how GameObjects attach to each other.
(E)Overlays contain the basic tools for manipulating the Scene view and the GameObjects within it. You can also add custom Overlays to improve your workflow.
(F)The Inspector Window allows you to view and edit all the properties of the currently selected GameObject. Because different types of GameObjects have different sets of properties, the layout and contents of the Inspector window change each time you select a different GameObject.
(G)The Project window displays your library of Assets that are available to use in your Project. When you import Assets into your Project, they appear here.
(H)The status bar provides notifications about various Unity processes, and quick access to related tools and settings.