An analogy for smooth endoplasmic reticulum are the halls of a factory through which information passes. The information in the case of a cell is messenger RNA.
A cell is analogous to a factory. Raw materials go into the cell or a factory to produce goods, and the goods depend on the type of cell. For instance, a cell in the pancreas produces insulin, a specific item that has a specialized use. In order to produce insulin, this factory takes in the raw materials of oxygen and nutrients.
The parts of a factory have their equivalents in cells. Cell membranes are like walls, separating each part of the factory or cell. The nucleus of the cell is the headquarters or main office, where the controls are situated. The DNA, or the factory plans and manuals kept safely in the main office, are the rules that govern how the products are to be produced. These plans are copied and passed out to the workers as mRNA.
While the smooth endoplasmic reticulum are the hallways through which messenger RNA travels to move information, the rough endoplasmic reticulum is the assembly line where the workers or ribosomes assemble the products, which are the proteins. Raw materials are kept in the stock room, or cytoplasm, taken out by the tRNA, or stockroom helpers, when they are needed on the assembly line.