What is exact meaning Windows NT 3.51 title bar buttons? Arrow up is maximize and arrow down minimize? And left button is close? Its my assumption right?
The upward-pointing arrow does indeed maximise the window, and the downward-pointing arrow minimises it.
The “minus” provides access to the window menu; double-clicking it will close the window. The menu for an application window is this:
The menu for an MDI document window (such as a program group in Program Manager) is this:
Applications can add their own entries to these menus.
These exact buttons were used in Windows 3.0, Windows 3.1 (and variants), Windows NT 3.1, Windows NT 3.51, and OS/2 1.3. I think the two menu buttons are supposed to be reminiscent of their keyboard short-cuts, AltSpacebar and Alt-.