Mulled windows

[scottbama]

I am building a small home and the plans call for two windows to be mulled with a 2x4. Not exactly understanding how this works or how to frame the wall to accomodate...please help. (FIRST OF MANY QUESTIONS TO COME I AM SURE)   

[Redoverfarm]

If they are side by side then there needs to be a mullion strip which is just a piece of trim to cover the connection between the two windows.  I am assuming that from the discription you use a piece of 2X4 between the two to make that union of the two windows. Tried to find a disgram but this is the only thing I found.

http://www.simonton.com/TopMenu/Press/Press/To+Mull+or+Not+to+Mull.htm