That is the formula to find the volume of a sphere. It's best to just memorize it as it is hard to come up with. The (4/3) is a constant (it is always that fraction). Pi is also a constant but it is a never ending decimal number so they use the Greek number pi to represent it. Most schools use 3.14 to equal pi but some just use 3 so be sure to check with your teacher. The r here is referring to the radius of the sphere which is the measurement from the center out to the edge. To find the volume you need to multiply (4/3) times Pi times (the radius squared)