You can navigate menu using several keystroke shortcuts
For each item having underlined letter or number you can press Alt + underlined character to perform its action or expand submenu.
For each active submenu item having underlined letter or number you can press either Alt + underlined character or simply underlined character to perform its action or expand submenu.
If there is active item, you can navigate menu by pressing arrows, Esc, Enter or Space buttons.
You can access each menu item just by pressing Tab key several times.