The main function of the Golgi apparatus in a cell is to modify, sort, and package proteins and lipids. After synthesis in the endoplasmic reticulum, these molecules are transported to the Golgi apparatus, where they undergo further processing, such as glycosylation. Once modified, the Golgi apparatus packages these substances into vesicles for transport to their final destinations, which can be within the cell or for secretion outside of it. This organelle is essential for ensuring that proteins and lipids reach the appropriate location and function correctly.