The first PC keystroke combination is for use when you have several programs open on your PC at the same time, and you are toggling between these programs, usually to share data or refer to needed information (say on your Internet browser).  Here is how it works:

 

Hold down the "ALT" key, and then hit the "Tab" key.  Windows will then bring up a small window showing icons of all of the active desktop programs that are currently running.  Keep holding down the "ALT" key, and hit the "Tab" key again, and the window will "scroll" over and highlight the icons of each of the active running programs.  If you then release the "ALT" and "Tab" keys when it hits the icon of the program you would like to jump to, your computer will jump to that selected program. 

 

Try this combo -- if you are doing any data or information sharing between open programs on your desktop, this keystroke combo can definitely save you some time vs. using your mouse to do the same thing. 

 

And if you'd like to close any of these programs once you get the data or information that you need, simply hit "ALT-F4".  That will immediately close whatever program you are actively working in.  That can save quite a bit of "mouse time" too!  Enjoy!