The role of the Golgi apparatus in a cell is to modify, sort, and package proteins and lipids produced in the endoplasmic reticulum (ER) for secretion or for use within the cell. This organelle is composed of a series of flattened, membrane-bound sacs called cisternae. Through processes like glycosylation, the Golgi modifies proteins with sugar groups, which can be crucial for their function. After processing, it dispatches these biomolecules to their appropriate destinations, ensuring proper cellular processes and function.