1) Attachment: the virus meets and then binds to a cell surface receptor, this explains why viruses often only infect certain species or tissues eg liver compared to neurones

2) Penetration and uncoating: the virus is enveloped by an endosome and is degraded and its nucleic acid escapes into the cytoplasm, no infectious virus remains

3) Formation of messenger RNA: Viruses have their own polymerase proteins which force the cell to make a
huge amount of viral mRNA and also nucleic acid.
This may involve steps which the host cell cannot do e.g. RNA to mRNA or RNA to DNA.

DNA viruses make mRNA in the cell nucleus.

RNA virus make mRNA in the cytoplasm.

Retroviridae are the exception. They transcribe double-stranded DNA which is then ligated by a viral integrase into the host cell chromosome as a chain of viral genes.