The function of the Golgi apparatus in cellular processes is primarily to modify, sort, and package proteins and lipids for secretion or use within the cell. After synthesis in the endoplasmic reticulum, proteins are transported to the Golgi apparatus, where they undergo various modifications, such as glycosylation. Once processed, the Golgi apparatus sends these molecules to their designated locations, either inside the cell, like lysosomes, or outside the cell via vesicles. This organelle is essential for the proper functioning of cells, ensuring that proteins are delivered efficiently.