The endoplasmic reticulum (particularly the rough endoplasmic reticulum) has ribosomes attached to it, a type of organelle that synthesizes protein. It also itself folds proteins in sacs on its surface called cisternae.
The question, however, most likely is referring specifically to ribosomes, as these are the organelles primarily responsible for the production of proteins. The endoplasmic reticulum is mostly to assist the ribosomes and transport the proteins once they are properly folded.
