What is Endoplasmic Reticulum (ER) and what is its role?

It is a sub cellular organelle that is attached in part to the nucleus. It has two parts: the smooth endoplasmic reticulum and the rough endoplasmic reticulum. The Rough Endoplasmic Reticulum is studded with ribosomes that synthesise polypeptide chains and secrete them into the rough endoplasmic reticulum. The role of the RER is to modify the shape of the polypeptides supplied to it. The Smooth Endoplasmic Reticulum has no ribosomes on its surface and instead deals with lipids and synthesis of steroid hormones. If you need any more clarification on this send me a message :)