The Window of Windows
In each major window, you will see three boxes in the upper right corner. The box with the small X at the far right closes the window and stops the program which it represented from running, and the program's icon is removed from the active area of the Task Bar. The box in the middle, which has either one or two squares in it, is a control which toggles (switches back and forth) between full screen and partial screen window size. The left box has a minus sign in it and will cause the window to minimize; the window is removed from the desktop but the program it represents continues to run and its icon remains in the active area of the Task Bar.
Programs which are running can also be controlled from the blocks in the active area of the Task Bar. Clicking the block or icon will toggle the program between being active and minimized. Right mouse clicking the icon or block will bring up a menu, the selections in which vary depending on the program, but almost always have a "Close" or "Exit" selection to close or stop the program ... And clicking the Show Desktop icon in the left part of the quick launch area of the Task Bar will minimize all running programs so as to clear the desktop.
A program cannot perform any functions unless it is running, and closing a program stops it from running ... For example, an email client which you set to automatically check for new email every 5 minutes can only perform that function if it is running, and it is running only if it's icon is present in the active area of the Task Bar.
When a window is in partial screen mode, it can be moved to any location on the desktop by grabbing the title bar of the window with the left mouse button and dragging the window to the desired location. Also, the size of the window can be changed by grabbing any edge or any corner of the window with the left mouse button and dragging it to resize the window.
It might be noted here that most functions mentioned in these lessons can be done without the mouse, using the keyboard exclusively, but that is for more advanced study. What I have to do is stay on course or we get into all kinds of discussions.