Viral structure and function go together since viral proteins, like all proteins, do particular jobs based on their shape. There may be proteins, such as glycoproteins, which help the virus enter the host cells. Other proteins are able to do jobs such as reverse transcription based on their shapes. The shape of the DNA or RNA bases in the viral genome determines the information contained and what can be done with that information, just as in a living cell. In this way viruses are like subsets of a living cell, which is one theory for their origins.
Work Step by Step
The thing here is to see that structure = function always in biology, whether one is looking at a living thing or something which interacts very closely with a living thing such as a virus.