The mRNA transcript that is produced in the nucleus is in immature form, it had to get matured, and then its capping and tailing is done. 5' cap is added and a poly A tail is added at 3' end of this mRNA. This helps it to get matured. moreover for its maturation the non-coding regions (introns) are removed and exons are packed up again to form a mature mRNA.
This mature mRNA then proceeds to its way to the ribosomes for translation of proteins.
