The ribosomes manufacture proteins for the cell and the organism. This process is called protein synthesis. Basically the DNA sends mRNA to the ribosomes to "tell" the ribosomes what protein to make. The proteins are then sent to the rest of the cell via the endoplasmic reticulum or stored there until needed. The ribosomes need the endoplasmic reticulum to transport the proteins to their designated places. If not, the proteins would just be floating about in the cell.