mRNA carries the code that was transcribed from DNA out to the ribosome to form the correct amino acid chain. So, yes, in a way mRNA is a messenger to the ribosomes since DNA cannot leave the nucleus.
A 5' cap and a 3' poly-A tail must be added. Then the pre-mRNA must be spliced. After this it is called mRNA and is ready to be transported to the cytoplasm for translation.