When is mRNA used?

Messenger RNA, also known as mRNA, is made in the nucleus of a cell, and then exported to the cytoplasm where the translation machinery which makes proteins, binds to these mRNA molecules and reads the code on the mRNA to make a specific protein. 

The mRNA is used to make new protein by your cells. This process is called translation and happens in the cytoplasm. One mRNA is specific for one protein.