The main function of the Golgi apparatus in cells is to modify, sort, and package proteins and lipids synthesized in the endoplasmic reticulum (ER) for secretion or use within the cell. It acts as a processing center where modifications, such as glycosylation, occur. The Golgi apparatus produces vesicles that transport finished products to their designated locations, including the cell membrane or lysosomes. Additionally, it plays a role in the synthesis of polysaccharides and can also be involved in cell signaling. Proper functioning of the Golgi apparatus is critical for maintaining cellular organization and communication.