Calla Lily Plant
What do I do with the growth in the base of the flower?
Not sure what you mean. The growth at the base of the flower stem, from which all the stems and leaves arise, is the rhizome, or underground stem. This is the part you divide to make more plants, or dig up and overwinter inside if you live in a cold area, then plant again in the spring: This article has information https://www.gardeningknowhow.com/ornamental/bulbs/calla-lily/growing-calla-lilies-and-care-of-calla-lilies.htm
It occurs to me that you might mean the rod-like shape around which the white petal curls. That is called the spadix, and it contains the actual flowers, masses of extremely tiny little things. The white "petal" is not a petal but a modified leaf, called a bract or spathe