Viruses form a shell around themselves called a capsid. This shell, or capsid, protects the viruses genetic material, or RNA, from intruders.
The most interesting part about the capsids is how they are formed. Like all DNA or RNA molecules, they include instructions for their replication. Ribosomes take the instructions stored in the DNA or RNA to build more of those same molecules. But viruses have a limited amount of storage, which means the instructions held in their RNA cannot have complex assembly steps.
Instead, they have a clever set of simple instructions that given enough time and chance, can form protective shells. Steven Mould does a much better job explaining it here:
