The RNA or DNA helps the virus take over the the cell it infects. The RNA or DNA contains the information that eventually tells the cell to make more viruses. The protein coat protects the RNA or DNA from being destroyed and helps the virus to attach to the cells it infects. A good place to look at some nice simple cartoons of viruses are found in Baron's online Medical Microbiology textbook. A really good introduction to what viruses are can also be found in this online text.
Viruses come in different basic shapes.
The most fantastic site I have found thus far is The Garry Laboratory Homepage . This site contains information for experienced virologists and for people wanting to know about viruses. Truly, a must see site. Especially, their extensive links page. Another good site for information on viruses is called the Universal Virus Database .