This screen allows you to launch multiple simulations.  This is the quickest way to see the effects of different copper areas.  The screen shows the different copper areas which are available for simulation.  Only the largest copper area is actually available on the Build It board which can be purchased in the Build It section of WEBENCH 
 

A. Click "Simulate Checked Copper Boards" to launch simulations for each of the checked boxes below. B. Click on a check box to select a copper area for simulation.  Multiple boxes may be checked at once.