Composition or also known as rule of third is a technique used by many expert and beginner photographers to create an effective but simple image from a standard background which creates a nice look to every image like the images below.
Composition is effective when the position of the object is in a certain position that it catches the viewers eyes this is called the sweet spot on the diagram above where the 2 lines meet or the perpendicular spot on the picture is where the sweet spot is and this has been scientifically proven that the cross section of the picture is where you brain is drawn to.