What is balance? Balance is the use of arranging shapes, subjects, colors, and tones to make an image feel even and pleasing to the eye. Eg.: Symmetrical balance is when both sides of the photo hold equal weight. Asymmetrical balance causes the viewers eye to move back and forth between elements.
The pictures above are both display color balance because of the pop of bright color that enhance the photo. For the left, the bright green grass, and for the right, the red effect.
These two photos display subject balance. The left has the car in the foreground with the airplane in the background, balancing the two. The right has the tree in the foreground with the barn as the subject in the background.
These photos display symmetrical balance. For the left, both sides hold equal balance. For the right, both towers hold equal balance.
Both these photos show asymmetrical balance. On the left, each side has a different kind of feel to it, making your eyes go back and forth between the two sides. On the right, two different structures on each side of the photo add the extra effect that a balance photo should do.