For those of you who lack the dexterity (or are loosing it) to operate a mouse efficiently, here are a few keyboard shortcuts which will save you time.  The spacings are to group them by similar function.

Note: Substitute the "Apple" key for "Ctrl" on Macs.

Editing text

Keys:    Function:
Ctrl + X   Cut      \
Ctrl + C   Copy   - Note that these three are neighbors on your keyboard.
Ctrl + V   Paste  /

The above work with entire files as well as text

Ctrl + Delete = deletes whole words
Ctrl + Backspace = deletes whole words
 

Navigating text

Ctrl + Up or Down arrow = jump paragraph
Ctrl + Left or Right arrow = jump over a word
Ctrl + Home = top of page
Ctrl + End = bottom of page

Common sense "initials" of their function.

Ctrl + N   New file or folder
Ctrl + O   Open a file in the application
Ctrl + S   Save
Ctrl + P   Print

Ctrl + Z   Undo (takes back an error such as the accidental deletion of a file)
Ctrl + Y   Redo (takes back an error in taking back an action)

Ctrl + Q   Quit
Ctrl + ?   Help (also, F1)
Ctrl + F   Find (search for text within a file)

Enter      Activates highlighted button
 

In most word processors:

Keys:    Function:
Ctrl + B   Bold
Ctrl + I    Italics
Ctrl + U   Underline

Ctrl + F   Find word
Ctrl + H   Find and Replace (swap one piece of text for another)
Ctrl + Z   Undo
Ctrl + N   New document
 

PC Exclusives (i.e., not for the Mac):

Alt    Activates the menu
Alt + F4   Close window or application

Netscape/Explorer stuff:

Spacebar   Page down
Alt + Left Arrow  Previous page
Alt + Right Arrow  Jump back to a later page
Alt + D   Bookmark current page

The Windows Key

By itself: Opens the "Start" menu which you can then navigate with the arrow keys

Windows + E   Opens "File Explorer" (a better tool for navigating your files than clicking "My Computer" on the desktop)