To demonstrate this in photography, see the graphic below. One image naturally follows the rule of thirds and becomes even more visually appealing when it is cropped. The other image is not naturally set up to follow the grid, but after it is cropped, it does become a more interesting picture.
You can use this same principle in design. I use iWork's Pages (Mac) for most of my designs. It is very similar to Adobe's InDesign software, which I used in journalism. You can follow the rule of thirds in any design software, including Microsoft Word. However, using Pages and InDesign make it easier for you to create a grid that you can see, but will not print. In both programs, just place your cursor in the ruler, then hold it down and drag your cursor to the place you want the line. Once you start dragging, a blue line will appear.
|Start with a blank document in Pages (or InDesign).|
|Place your cursor in the ruler, then click and drag it. A blue line will appear. Unclick when the line is where you want it.|
|To make the horizontal lines, drag from the top ruler.|
|Repeat this step until you have nine equal parts.|
cover page and a page from one of my Powerpoint presentations that demonstrate the rule of thirds. Notice that the cover page does not have any dynamic images, but because the title is placed on the upper horizontal line, it is more appealing. You can use lighting effects to also draw the viewer's eye to one of the focal points, as demonstrated in the presentation page example.
This does not mean that you should always follow the rule of thirds. But if you are struggling with design and want to try something that will catch the viewer's eye (perhaps make your pages more "pin-worthy" on Pinterest), try this method out and see if it works for you. Good luck!
You can download this tutorial FREE in my teacher store, which includes two gridline .png graphics and additional tips: