All the translation (making of proteins) is done by the cell's ribosomes (this for almost every viruses) from mRNA strands as the cells do everydays to make proteins.

But the replication and transcription (making copies of the full length RNA genome and some mRNA copied from parts of it) is achieved by a viral polymerase, a RdRp.

This is for RNA viruses. Many DNA viruses do something along the same lines, but some do not and make their genome enter the cell nucleus to exploit either its DNA replication machinery or its DNA->RNA transcription machinery, or both.

Retroviruses are some kind of hybrid between the two strategies.