Structure
A virus is not really a living thing. It can not perform basic processes common to most living things. For example viruses do no respire, neither can they reproduce outside a host cell.
Replication
In order to replicate or reproduce, a virus requires a host, which makes them a parasite because they require a host in order to survive.
The virus is chemically attracted to the host cell.
Envelope joins with the cell membrane, and the virus enters the cytoplasm and then nucleus where the capsid breaks down.
The viral RNA is used to take control of the cell.
Copies of RNA are made in the nucleus and capsids are made in the cytoplasm.
The capsids enter the nucleus where they enclose the RNA.
The viruses cause the membrane to break open and they leave the cell, and in so doing take some of the membrane as an envelope.
The cell dies and each new virus can infect another cell in the same way, Thus creating a cycle of viral activity.