What is the function of rough endoplasmic?

Answer 1

In this question it seemed like you were referring to the organelles on the rough endoplasmic reticulum which, by the way, are called ribosomes.

Ribosomes binds to mRNA (messenger RNA) and assembles protein using tRNA (transfer RNA) complex.

They are also the sites responsible for protein synthesis. It's been described as a kind of platform where proteins are built. They use the RNA copy of a gene to read it like a 'copy of a blueprint' to construct the protein needed.

If that is not what you were looking for then this is the function of the rough endoplasmic reticulum:

The rough endoplasmic reticulum is a membranous structure that associates closely with the nucleus. Embedded in the membrane of the structure are ribosomes, this is what gives the "rough" appearance. RNA passes through the ribosomes where its sequence of nucleic acid codes for specific amino acids to be joined up in a specific order. The route through the ribosomes for the amino acid takes them into the membranes of the reticulum where they can be kept together. They are then moved of in vesicles formed from the ER membranes to the Golgi Apparatus to be packaged and processed.