Shading correction is a function to correct light falloff at edges, which is a characteristic of a lens, making an area around the object darker. Use two parameters to correct shading.
On lens, light volume is decreasing toward the periphery area. The light volume is larger in a wide-angle lens and smaller in a telescopic lens.
You can use this function to adjust the level of correction for the following cases. The case you want to remain the shading effect without complete correction since the shading is one of the effects which is unique to a lens. Or a case that a bright object is on the periphery of a photo and it is lost when you make corrections. You can also increase the shading level by setting minus value. Use the value to emphasize the center area on purpose by darkening the periphery, or to make the background quiet.

Chromatic aberration correction is a function to correct false coloring on the edge around an image, which is a characteristic of lens. Chromatic aberration is caused by the difference in image formation ratio of light (red light, green light, and blue light) incoming to a lens. Chromatic aberration correction is performed by changing R image formation ratio and B image formation ratio slightly.

Distortion correction is a function to correct distortion aberration, making the straight line distorted.
This parameter in turn to correct most of distortion of photo lenses, which can be corrected almost completely. If you use this parameter properly, it is possible to correct or modify a lens having complicated distortion aberration (called hat shape type).