File → Open (-O)

File → Close (-W)

Option-click on the close window button.

If there are changes that need to be saved in any of the windows being closed, you will be prompted to save. Either hit Return to save the changes, or enter -D to invoke the Don't Save button.

Window → Minimize Window (-M)

Double-click on the window's titlebar.

Option--M

With some applications, Option--M may function differently. For example, issuing Option--M in Microsoft Word (Office v.X) will open the Paragraph format window (Format → Paragraph). Instead, you can minimize all of Word's windows by holding down the Option key and double-clicking on a document's titlebar. To be safe, you should save changes to the file before trying to minimize all of the application's windows with Option--M.

Shift-click on the minimize button in the window's toolbar. (This works in reverse, too; shift-clicking a minimized window icon in the Dock opens it up slowly.)

Shift--click on the minimize button.

Option--click on the Dock icon for the application you're using; the open windows for all other active applications will instantly hide. To bring another application's windows to the front, click on that application's Dock icon. To unhide all the other windows, select Show All from the application menu (e.g., Finder → Show All).