The easiest way to describe an IWB is to say that it is a large computer touch screen, a virtual filing cabinet of resources. The board can be used as a normal classroom board but can also be used to design classroom activities such as matching or gap fills.
Many schools have IWB activities available for the course and is constantly developing more. Basically, any activity you can do on a computer you can do on an IWB, the main restriction is your own imagination!