Closing multiple windows all at once:
Hold the CTRL key down and click on each of the tabs in the Task Bar (at the bottom of the screen) that you want to close. Then right click on one of the selected tabs and select "Minimize Group" from the menu that appears:
You might want to try the other options on this menu just to see what they do also (Cascade, Tile Horizontally, Tile Vertically). Selecting "Close Group" will close all the windows you have selected. As you get used to using the computer you inevitably get used to having more and more windows open at once. This little trick can help you manage them more efficiently.