All it's saying is that for every unit (x) that the dimension of an object increases, then its volume will be increased by x^3. For example, say a you have a cube whose sides are equal to x and volume is x^3. If you increase the size of the cube's side to say (x+1), then the volume will increase (x+1)^3. Same for a sphere if V = 4/3pi*r^3. If you increase r to (r+1), then the volume increases by (r+1)^3.