the Windows key
Bypasses the active application and communicates commands directly to the operating system.

Windows key
(by itself):

calls up Start menu & taskbar
[or Ctrl-Esc, if you’re using an older keyboard]

Win-M:

Minimizes all windows (& shows desktop)

Win-E:

runs Windows Explorer

Win-F:

Windows file "Find" dialog

Win-L:

Log out immediately

the "Application" key

calls up "context" menu; equivalent to right-clicking on an object
various functions ... incl. ability to Cut/Copy/Paste files from one place to another ... change file Properties (e.g., make Read-only) ... send a file to a chosen application ... and other commands, depending on the situation

(Shift-)
Ctrl-Tab:

Alt-letter:

opens application’s pull-down menu
e.g., Alt-F = File menu

then, press underlined letter in menu item to complete the command
e.g., Alt-F, S = File, Save
(this is in addition to the usual single-key shortcuts, such as Ctrl-S = Save)

Also note that the cursor keys can "traverse" menus, left/right/up/down; Return or Enter to progress further; Esc to retreat one step; or press underlined letter to activate that menu command.

Alt-spacebar:

accesses application menu
e.g., Alt-spacebar, N = miNimize the current application;
e.g., Alt-spacebar, X = maXimize the current application

Alt-hyphen:

accesses document menu (within parent application)

Alt-F4:

quits & closes the current application or thread

(Shift-)Alt-Tab:

Hold down the Alt key, then tap the Tab key repeatedly ...
then, when the icon for the desired task is highlighted, release the Alt key.
(Note that you can use this to easily toggle back & forth repeatedly between two specific tasks).
Using the Shift key at the same time cycles in the opposite order.

Alt-Esc:

Aborts an Alt-Tab in progress ...
while still holding the Alt key, release the Tab key, then press Esc instead.

Windows key + E:

runs Windows Explorer (from anywhere)

[numeric keypad]
+, *, - :

expand, expand all, collapse listing
(for a drive or file directory in the left-hand pane)

Return/Enter:
(in right-hand pane)

opens highlighted directory

Backspace:

moves up to parent directory

F5:

forces file listings to refresh and resort
(i.e., if they didn’t update immediately after changes)

View > Options:

various choices on how to display files, extensions, etc.; and lets you specify the default application launched for various file types

Alt-Return/Enter:

calls up selected file’s Properties dialog
(equivalent to Mac’s "Get Info" box)

Edit > Undo
or Ctrl-Z:

to Undo the last file operation (copy / move / rename / delete):

... to copy or move file(s), or create a shortcut: right-click and, still holding down the mouse button, drag & drop file(s) to their destination — to get a pop-up menu of copy / move / shortcut choices.

F1:

Help (often context-sensitive)

F2:

Rename selected file or folder
(can also use to copy text from, or paste it into, a file/folder name or portion thereof) ... ESC to cancel

Print Screen key:

Alt-Print Screen key:

copies screen shot of entire screen to Clipboard

copies screen shot of active window to Clipboard

Ctrl-Insert, Shift-Delete, Shift-Insert:

alternatives for Copy, Cut, Paste

Home/End;
Ctrl-Home/End:

jumps to beginning/end of line;
jumps to beginning/end of document

Ctrl-left/right arrow:

skips to the beginning of previous/next word

Ctrl-up/down arrow:

skips to the beginning of previous/next paragraph

Shift-

in combination with one of the above (and/or with one of the four arrow keys), highlights the intervening section of text

(Shift-)Tab:

moves cursor to previous/next field

(Shift-)
Ctrl-Tab:

cycles through tabbed dialog pages
(also, sometimes Ctrl-PgUp/PgDn):

Spacebar:

presses selected button,

or toggles checkbox